Nouns referring to nationality are often different from the corresponding adjectives.

• Ellis considers himself a typical Welshman. (NOT … a typical Welsh.)
• She's married to a Spaniard. (NOT …  a Spanish.)

We usually put descriptive adjectives before classifying adjectives.

• An old political idea (NOT A political old idea)
• The latest educational reform (NOT The educational latest reform)

We don't usually use too before adjective + noun.

• The problem was too difficult. (BUT NOT It was a too difficult problem.)
• I put down the bag because it was too heavy. (BUT NOT I put down the too heavy bag.)

Eventually means 'finally', not 'possibly' or 'perhaps'.

• It took a long time, but eventually he finished his studies.
• I'm not sure what I'll do next year. Perhaps I'll go to university if I can get a place. (NOT Eventually I'll go to university …)

We don't usually put an adverb and its complement together before a noun.

• We're looking for people who are skilled in design. (NOT … skilled in design people.)
• He has a difficult accent to understand. (NOT … a difficult to understand accent.)

Asleep and afraid are not normally used before nouns.

• He had the innocent expression of a sleeping baby. (NOT … of an asleep baby.)
• In the house, we found a frightened child hiding in the kitchen. (NOT … an afraid child.)

Actually means 'really' or 'in fact', not 'now'.

• She said she was 18, but actually she was 15.
• In 1900 the population of London was higher than it is now. (NOT … than it actually is.)

We usually use over, not across, to mean 'on/to the other side of something high'.

• Why are you climbing over that wall? (NOT … across that wall?)
• I threw his keys over the fence, where he couldn't get them.

Words like President, King, Doctor in titles have no article.

• President Nixon resigned over the Watergate scandal. (NOT The President Nixon …)
• I'd like to see Dr Franklin. (NOT … the Dr Franklin.)

Weather is uncountable.

• We had terrible weather last week. (NOT … a terrible weather …)
• I hope we get good weather at the weekend.

With abbreviations, the difference between a and an depends on pronunciation, not spelling.

• She’s a US citizen. (NOT She’s an US citizen.)
• Would you like to be an MP?  (NOT … a MP?)

• I’d like to be able to sing. (NOT … to can sing.)
• When will you be able to meet us?

Travel is normally uncountable.

• I like travel.
• We went on a trip/journey to the Antarctic last spring. (NOT We went on a travel …)

We use because, not as or since, if the reason is the most important part of the sentence.

• Why am I leaving? I’m leaving because I’m fed up. (NOT I’m leaving as/since I’m fed up.)
• They’re laughing because they think your hat’s funny.

When which? what? or who? are subjects, we make questions without do.

• Which costs more - the blue one or the grey one? (NOT Which does cost more …?)
• What happened to your car? (NOT What did happen to your car?)
• Who phoned? (NOT Who did phone?)

We drop articles in some common expressions with school and bed.

• Why isn’t Angela at school today?  (NOT …  at the school today?)
• I want to spend a day in bed. (NOT... in the bed.)

We don’t use some if we know the exact number.

• You’ve got beautiful fingers. (NOT … some beautiful fingers.)
• A mountain bike needs to have strong wheels. (NOT …  some strong wheels.)

Advice is uncountable.

• Can you give me some advice? (NOT … an advice?)
• My father gave me three pieces of advice. (NOT …  three advices.)

We use any, not every, to say ‘one or another’.

• ‘Which newspaper would you like?’  ‘It doesn’t matter. Any one.’ (NOT …  every one.)
• ‘When would you like to come to dinner?’  ‘Any day is OK.’

We say that somebody is good, bad, clever etc at something.

• My sister is very good at maths. (NOT … good in maths.)
• I’m not very clever at languages.

Don’t put articles and possessives together before nouns.

• She’s  a friend of mine. OR She’s my friend. (BUT NOT She’s a my friend.)
• Peter’s lost his keys. (NOT … the his keys.)

We use either, not any, to talk about two people or things.

• I can write with either hand. (NOT … with any hand.)
• ‘Do you prefer Monday or Tuesday?’  ‘Either day will do.’

We don’t usually use other with uncountable nouns.

• Can I have more rice?  (NOT … other rice?)
  

• Perhaps we should use different oil.  (NOT … other oil.)
  

For more details, see Practical English Usage Third Edition 54.

Don’t put articles and possessives together before nouns.

• She’s  a friend of mine. OR She’s my friend. (BUT NOT She’s a my friend.)
• Peter’s lost his keys. (NOT … the his keys.)

We use either, not any, to talk about two people or things.

• I can write with either hand. (NOT … with any hand.)
• ‘Do you prefer Monday or Tuesday?’  ‘Either day will do.’

We don’t usually use "other" with uncountable nouns.

• Can I have more rice?  (NOT … other rice?)
• Perhaps we should use different oil.  (NOT … other oil.)

Whose means ‘who is’ or ‘who has’; whose is a possessive.

• Who’s that? (NOT Whose that?)
• Who’s taken my keys? (NOT Whose taken my keys?)
• Whose coat is that? (NOT Who’s coat is that?)

We don’t use it … + infinitive with allow.

• Smoking is not allowed. (NOT It is not allowed to smoke.)
• We weren’t allowed to use calculators in the exam. (NOT It wasn’t allowed to use …)

Use superlatives to compare people and things with the groups that they belong to.

• Sandra is the tallest of the five girls. (NOT Sandra is the taller of the five girls.)
• I think I’m the oldest person in the class.

In affirmative sentences we generally use "a long time", not "long", except in a very formal style.

• We waited a long time, but she didn’t come. (NOT We waited long, but …)
• It will be a long time before we invite her again.

We don't use "on the contrary" to give another side of a question

• It's hard work. On the other hand, it's interesting. (NOT on the contrary, it's interesting.)
• She's very bad-tempered. On the other hand, she's generous.

Comparatives are made with "more" or "er",  but not both.

• The weather is getting colder. (NOT … more colder.
• Please try to be more polite. (NOT … more politer.)

We say "come from (present)" to give our town, country etc of origin.

• Sarah comes from Texas. (NOT Sarah came from Texas.)
  Where do you come from?

We prefer "closed", not "shut", before a noun.

• When I talk to you, I feel as if I'm standing in front of a closed door. (NOT … a shut door.)
• He's got a closed mind. You can't tell him anything.

You borrow something from somebody.

• I borrowed the money from my mother. (NOT I borrowed my mother the money.)
• Can we borrow some glasses from you?

"News" is singular

• All the news is bad. (NOT All the news are bad.)
• BBC Radio 4. Here is the news.

"Before" (meaning ‘before that') follows an expression of time.

• Last summer, I decided to go and visit the town that I had left eight years before. (NOT … before eight years.)
• I had already met her once, about three years before.

After the verb "lack", no preposition is necessary.

• The soup lacks salt. (NOT … lacks of salt.)
• It's a good novel, but it lacks structure.

"Because" is a conjunction; "because of" is a preposition.

• We cancelled the match because it rained. (NOT … because of it rained.)
• We cancelled the match because of the rain. (NOT …because the rain.)

Expressions like "in three hours" time refer to the future.

• We'll need the report in two weeks' time. (BUT NOT He wrote the report in four hours' time.)
• I'll see you again in a month's time.

"As well as", with a similar meaning to "not only... but also", is normally followed by an "ing" form.

• As well as breaking his leg, he hurt his arm. (NOT As well as he broke his leg...)
• He works full time as well as bringing up three children.

We say "as usual", not "as usually".

• Let's meet tomorrow at 10.00, as usual.
• John's late as usual.

After "as long as", use a present tense to refer to the future.

• I'll remember this holiday as long as I live. (NOT ... as long as I will live.)
• You can have my bike as long as you bring it back tomorrow.

We use "when", not "as" or "while", to talk about ages and periods of life.

• When I was 14 I first got interested in archaeology. (NOT As/While I was 14...)
• We lived in London when I was a child. (NOT ... as/while I was a child.)

After "look", we use "at" with an object.

We don't usually use "before" to mean "in front of".

• You can park in front of the station. (NOT ... before the station.)
• There's a big tree just in front of our house.

"Far" is unusual in affirmative sentences, except in a very formal style.

• We live a long way from here. (NOT USUALLY We live far from here.)
• It's a long way to Tipperary.

Don't use "every" to talk about two people or things.

• You can park on each side of the street. (NOT ...on every side of the street. )
• He was holding a glass in each hand.

"Tell" normally needs a personal object.

• He told us that he was going home. (NOT He told that he was going home.)
• I've told you everything I know.

We say something to a person.

• She never says 'Hello' to me. (NOT She never says me 'Hello'.)
• Andrew has said nothing to Peter. (NOT Andrew has said Peter nothing.)

Use "because" or "so", but not both together.

• Because the train was late I missed the meeting. OR The train was late, so I missed the meeting. (BUT NOT Because the train was late, so I missed the meeting.)

"Everything" is a singular word.

• Everything was broken. (NOT Everything were broken.)
• Is everything ready?

To say that something is not necessary, use "needn't" or "don't have to", not "mustn't".

• You needn't pay now; tomorrow will be OK. (NOT You mustn't pay now; tomorrow will be OK.)
• I don't have to wear a tie at work. (NOT I mustn't wear a tie at work.)

Indirect questions usually have the same construction as statements.

• I asked where her parents were. (NOT USUALLY I asked where were her parents.)
• The policeman wanted to know where I lived. (NOT ...where did I live?)

Don't use "could" to talk about something that you succeeded in doing.

• I managed to run 10 km yesterday in under an hour. (NOT I could run 10 km yesterday...)
• How many eggs were you able to get? (NOT ...could you get?)

"How long are you here for?" asks about the future.

• A) How long are you here for?                                                                                                                             
• B) Till Easter. (NOT 'Since Christmas.')

Use an "ing" form after "be / get used to".

• I'm used to driving in London now, but it was hard at the beginning. (NOT I'm used to drive...)
• I'll never get used to living in this place.

After "would rather", use an infinitive (without to) or a past tense, not a present tense.

• I'd rather stay at home this evening. (NOT I'd rather to stay at home...)
• I would rather you paid me in cash. (NOT I would rather you pay me in cash.)