it's not bad for a first model, but i'd suggest redoing the whole thing from scratch once you're don. Why? because most first models arent very accurate. As yours isn't. Don't get me wrong i like it so far, it's much better than my first model, but i see some problems. The handle for one, is too blocky, it doesnt look like something you'd like to hold. The front grip, looks like an mp5 front grip, but that's not really the way they are:

see? it slopes down to the lower part, as well it still slants like the other grips. It's not all perfectly round, or in two parts. So it's close, but it could be better.
I'd lower the cylinder poly counts they're wasteful, nothing should go over 10 sides, maybe 12 if you want, but nothing more. Clip thing already stated. and i'd look at making more detail in the body itself (what you have of it at least) add groves, releaf's you know, definition.
i do like what you've done though, and i think you're going to be great at modelling if you keep at it.