I find myself writing without contractions and I think that is due to my years of business communications and non-fiction freelance writing. But for the most part, we don't talk in formal English, we use contractions.
So I find myself going back and editing my dialogue, putting in the most common contractions. That's not to say I change them all. Sometimes you need to understand a statement is being made by your character. Other times you may have a character that uses formal English for various reasons. It's part of their character.
Here is a quote from the Tameri Guide for Writers :
A verb contraction shortens a verb or verb phrase, matching informal English speech. Contractions join with verbs or pronouns. Avoiding contractions when writing fiction results in stilted dialog, while using too many reduces the effectiveness of writing.
Ain’t is never the contraction for “am not” or “is not.” While some defend the use of ain't for “am not” as no more irregular than won’t for “will not,” no authority seems to accept this argument.What about your writing? How do you use contractions... or not?