First of all, all rodents are very sensitive. Just like cats and dogs, they need vet care and constant visual. If their water bottle is out of water, you can damn well bet they wont TELL you that. You have to see yourself. Rodents are prey animals, not pets, they don't make many noises and when they do you can pretty much bet something is seriously wrong. The only exception to this rule is "happy clicking" which you can barely hear.
And don't get me started on cages. I'll put it plain and simple. QUIT WASTING YOUR $40 ON SHIT CAGES AT THE STORE. They are NOT good for your hamster. Syrian hamsters (not teddy bear, panda, etc as pet stores label them to make you pay more) need 300 SQUARE INCHES minimum. Dwarf hamsters (Campbells, Chinese, Robovorski, or Winter White. NOT 'blueberry' 'russian snow' etc) need 200 SQUARE INCHES minimum- OH. And dwarf hamsters can squeeze out of 1/2inch openings through wire bars ;) Most pet store cages are lucky to have 100 SQUARE INCHES- IF that. It's exactly the same as if you were to lock your dog in a crate all its life- or YOU live in a CLOSET all your life. So before you go waste your money, go buy your dwarf a 10gallon tank or your Syrian a 20gallon and save your money. OR better yet, buy a bin ($15 max) at wal*mart and MAKE YOUR OWN CAGE :o

And then there's wheels. Don't get me started on wheels. Basically, if you own a hamster tape your wheel with duct tape. The picture on the right is of my hamster on his duct taped wheel. See how 1. its taped on the inside AND outside and 2. ITS BIG ENOUGH FOR HIM?
That leads into my second point. People buying wheels that are too small. People, Syrian hamsters need 7" wheels and dwarfs need 6" wheels. The bigger, the better. There should NOT be a bar going through the middle and their backs should NOT bend at all when they are running. If your pets (all rodents are the same for this rule) have a bent back when they're running, the wheel is too small. Also, gerbils need a bit bigger wheels because their tails will curl over their backs and cause issues with that.
Another thing, bedding. CEDAR AND PINE ARE THE WORST THINGS EVER. Ever. They cause respitory stress, UTI's, etc and can even lead to death. Not only that, but they smell like hell. Aspen, Carefresh, recycled paper type bedding, unscented toilet paper/paper towels/etc. ALL of those are FINE for bedding. But remember, hamsters like to dig. They need enough substance to dig down into. Gerbils need atleast 6" of bedding to make tunnels (gerbils will need to have timothy hay or shredded cardboard mixed into their bedding to help their tunnels stay open).
Roll about balls, avoid them at ALL costs. My gerbil, Tiki, was in a roll about ball in his previous home. He ran into the wall so hard going so fast he now has brain damage. Also, they cut off rodents' senses (hearing, smell, eyesight, etc) and stress an animal more than you could imagine.

I think that's all for now. If you have any questions, feel free to ask. Happy rodent owning!
And last, but not least. Join this forum and read all the stickies. They have great help.
http://www.hamsterhouse.com/forum/index.php