1) When I was taking an English course, the teacher once corrected me saying:
You shouldn't write don't, write do not!
Since then, I only write don't in informal cases: email to a friend, here, etc.
Do you think is it all right to write don't in a cover letter (for instance)?
Shall we write Do not if we want to make a good impression as saying that we have an excellent level of English, or all of this doesn't matter?
2) Another question is about the usage of Would like and 'd like. In grammars and websites about English language on internet they always say:
I Would like = I'd like
Then, when is the time to give examples they use 'd like in most cases.
E.g I'd like a cup of tea
Today I was doing a grammar exercise and the key answers usually have alternatives to include short forms - has not (or hasn't) etc. - but for would like there were not alternatives, the answer should be 'd like.
Is it old-fashioned to write:
I would like a cup of tea (?)