Actually, I'd advise avoiding both by using "need." Example: I'm in need of a good coat. (slightly old fashioned sounding) I have a need for a good coat. (slightly awkward and wordy) I need a good coat. (nice and simple) I hope that helps.

Do not be like a robot: english as many languages break its own rules just remember in which phrases correspond each word as you practices. I know that articles and those small words (of, for, in, at, on) are extremely difficult because in chinese you do not use them. but remember just memorized in which situations those word fits prefectly and if you dont remember dont worry a native speaker will understand what are you trying to say

Maybe this will help: http://forum.thefreedictionary.com/postst6025_The-difference-between--need-for--need-of--think-of--think-about.aspx