For me is double letters in words like different and support, I really don't know if there's a rule for it. Also, the verb do in past tense followed by another verb also in past tense, I know that's wrong but I keep making the same mistake >_<
I don't think anybody that wasn't born speaking a language should feel bad about their learning process, and if a native speaker ever makes fun of me for it I'll tell them: to go ahead and try to write a sentence in Spanish and we'll see about your grammar.