Never comb or brush your wet hair. Seriously, don't do it. It breaks the hair follicles and makes your hair fall out way quicker than it normally would. What should you do instead? Brush your dirty hair BEFORE you get into the shower and then once it's clean, just use your finger tips to get out tangles. Obviously this is easier to do if you use conditioner (side tip: only condition the hair that isn't on your scalp, 'cause if you condition your scalp it'll get greasier way quicker - only the ends need conditioning).
How do I know these things? Experience, son! My hair used to fall out like mad. For years. I only got a handle on this a few years back, and after trying these things there's no going back.
Also, if you have roommates, don't forget to clean out any hair in the drain after your shower. Blows my mind that people still don't adhere to this human courtesy. (I am in no way talking about my own roommates, they're wonderful. I'm talking to you other cretins who aren't doing this.)