No matter how much theory you know, there are always little problem solving tricks that most students need to be shown and go over to be ready to use on tests. Spend a lot of time on these. If your not sure what I'm talking about, think about the problem that stumped you for 20 to 30 mins or more and when you found the solution (either on you own, or someone showed you) you smacked your forehead and screamed "OF COURSE!" At the same time, it's the theory that will give you shot to suddenly come up with the solution to a type of problem that you might have forgotten about or never seen.
I usually spend about 30% of my time going over proofs and theory, and 70% going over specific problems that we seemed to spend a lot of time on in class or in the homework. It might not be the most balanced approach, but It's saved my ass more times then I can count.
Also, talk to your fellow students, if they seem concerned about something that your not, you may have missed something. Maybe your oversimplifing something, or maybe you just know it better then they do, but check it out. Never assume you are ready for a test, be paranoid until it's over
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Edit:
one other thing that has helped me out a lot. Get together with some weaker students to study. Answer their questions and show them how to do things. If you can easily tanslate what you know into language that they can understand, you have the subject nailed, if their questions throw you off your game, you still have some work to do. I can't tell you how many times a friend of mine has asked me a question that I couldn't answer without looking things up in the book, and then it showed up on the test. Honestly, if I hadn't made some truly epic stupid mistaks on tests, I would have 96% average on my general circuirts/digital logic tests. As it is, I've scored 88% to 92% on all 3 of them, so take my advice for what it's worth.