i think it really depends on what is your writing style.
but i would like to add/correct a few.
1. 'contractions are not necessary' and absolutely should not be used.
2. KISS (keep it simple stupid). the point of writing, for the most part, is to get as many people as possible to read you work. and by using big words, you may be limiting your audience. i know i get turned off to reading when every sentence i have to reach for a dictionary.
3. parenthetical marks can be used, but they show what ever information is inside of them, is not as important as what is out side of them.
4. learn the difference between their, they're, and there.
5. excessive use of profanity does 'suck'. but if that is who your character is, then use it.