I really enjoyed Micro and got an A. As has been said above, focus on Gram+ and Gram- first. That's what you will see most of. From what I've seen in clinicals so far, Staphylococcus aureus is the big bad monster of microbiology. Every one of my patients that has had an infection so far, has had a S.aureus infection. I know there are a billion other bad bugs out there, but that's the one I've seen exclusively so far. I found flashcards really helpful, honestly - but I know the helpfullness of flash cards depends on the person. I also focused a lot on the charts in the books. And as Zookeeper said, you *really* want to make sure you get the immune stuff. That will be much more helpful and important to know later on.
edited to add: also, google is your friend. I used google so much in Micro, if I just wasn't getting a concept. I like this website: http://www.textbookofbacteriology.net/
but if I had a question about a specific bacteria or test I'd google it. You'll find a lot of junior high and high school websites out there.... but sometimes those are the best ones, because it's presented with the understanding that the students are not experts.