I do, I do!

I got MGS2:S for Christmas but have not played it as I've been waiting for TTT. Well, I got TTT yesterday, and... DAMN I really suck at it. I get caught and usually killed at least 3 times per room, and I'm only in the 3rd or 4th one! I enjoy playing it, but I don't know what to do... I can sneak past guard ok, but the securuity cameras always spot me. I really like this game but just can't seem to get it. Can anyone help?!