Just take pictures of anything, remember with a digital camera all the pictures are free, I take pictures of insects and plants, scenic places, read the camera manual, get to know the camera and everything it will do. I love the closeup setting, its what i use for insects, i have some cool wasp and dragonfly pics. Know how to turn the flash off and on, all pics dont need flash. Download a program called Paint.Net and all the plugins, maybe the gimp too, it's nice to tweak pics now and then for improvement or artistic value. you may want pics to put on websites or forums or facebook and stuff. Pics can sometimes look better than the actual thing you took a picture of. Carry the camera with you when you go places, there may be a river or a creek or something. I myself will take pics of just about anything, Heres a pic of a wasp i took.
Well, most photographers have something that appeals to them as subject matter, you may not have found it yet? I really like doing pretty wide landscapes and also more macro shots of insects/flowers/and the like. Not huge on portraiture, though I do enjoy taking event photography when we have some kind of get together or performance.
Every picture doesn't have to be an art piece, you can just do event photography when your friends have meetups, pictures of food, or just pictures of you and your friends hanging out. The more you take pictures, the more you may find certain things catching your eye. You may see mundane objects in interesting light and think "hey, that'd make a really nice picture with this lens". Not everyone is going to find the same subject matter interesting, so I can't really tell you WHAT to take pictures of. I can give you suggestions for exercises in order to utilize certain techniques, but I can't really tell you what appeals to you.
" I suggest taking photos of boobs. (We were all thinking it) "
Haha so very true. But on a more serious note, I've never been one to buy cameras nor go out on missions specifically with the intention of taking pictures. Recently however, I have been taking more pictures with my Kodak Zi8, I live in Ireland and the scenery is pretty sweet although it does rain from time to time :) (nearly always raining). Just take the camera with you wherever you go and snap at anything which looks interesting. But more and more I've gotten into using my camera for video, I often take videos when I go somewhere now and i'm sure it's probably a nice break from taking stills. Heres a video I took while fishing with my friends off the south coast of Ireland near my house. I know it's not a top class video in terms of technique nor quality but I enjoy it.
Like @ Addfwyn said, some subjects will attract you more than others, once you found what it is, just get the right lens, and shoot. What lens do you have for now? Some lens are "all terrain" but are not really excellent at anything (but you can still have very decent shots). Anyway, you can start shooting random things (like I do), even if you do make any great shots at first, you'll still learn how to use your body/lens, learn what you can do, what you can't, and maybe what you're good at, and what you're not good at. Personally, I found that I'm bad at portrait... so for now, I don't do any. Shooting random things can sometimes get you some decent stuff: