My mom still gets mad when I get "I" and "me" mixed up. It still happens too often, giving her joy every time. It's the same thing in Portuguese. The big confusion is whether to say para mim or, para eu.
Once you know it you will never again get it wrong. It all comes down to this:
If you could have completed the sentence with a verb, then you must use para eu.
Let me illustrate what this means. Imagine your friend Mariana just bought you nice shirt to wear (usar):
You would have to use para eu in this case. Notice that there is a verb after the para eu.
And if there was no action (ie, no verb) at the end of the sentence, use para mim. Like this:
You might think that these mean the same thing -- and, in a way they could - but they do not. In this case the mim is receiving the action, not participating in it.