Try doing this with your hand. You'll notice that your pinky and thumb come really close together, and are actually almost the exact same length. Keep this in mind also when drawing different hand poses.

Ok last thing with the pinky, I promise hehe. If you do this with your hand, you can see the web of skin between the pinky and ring fingers. This is basically just to show you how the gaps between your fingers react to movement and stretching. Also, note how the flesh under the pinky bunches up and forms a bulge. Don't forget details like that. Your hand has the same mass no matter what position it"s in, and that mass has to go somewhere when the hand changes.

Now for grasping objects. This is kinda hard to do, so I suggest studying your hand holding an object before really trying to do this on your own, because most times, it'll come out horribly wrong. Imagine holding a steel pipe. If you are drawing a hand holding a steel pipe, do NOT make the hand conform to the pipe, because that doesn't happen in real life. Your hand is made up of bones, not mush, so when you grab something, the bones fold at the hinges, which makes for a more boxy look. Try drawing it that way. If you bring out the "boxiness" in a hand, it'll look better. Don"t "drape" the hand around the object it's holding, or that will make it look fake and just stupid looking. Look at the picture below.

Look at the stages of the hand closing. At first, the hand is open wide, fingers spread out. Next, it begins to bend. As soon as the the knuckles reach the end of their range of motion, they lock, which causes the bones leading from the knuckles to stop moving. But that's only the first joints in the fingers. Next, the rest of the finger keeps bending until the middle knuckles lock, and causes the rest of the finger to stop moving up to the tips of the fingers, where the last knuckles remain.

These are the knuckles near your fingernails, and they don't bend that much, but they do bend enough to allow you to tuck your fingers into your palm. Look at the last picture, see the tops of the fingers? They aren't rounded off, they form a right angle because the bones in your fingers are straight, and they lock at a hinge. Then, they bend off again at another right angle near the middle knuckles. That's why I refered to the hand as being boxy.

Ok, here we have a hand holding a pipe. Now, you'll notice it's not completely closed. After all, it's holding a pipe, which means that the fingers have to be opened up to allow space for the pipe to fit. The pipe is actually resting in the folds of the fingers, and not on the palm. So you can image the hand as being a cupped C shape, not a closed fist. And I actually screwed up in this picture. You aren't supposed to start the pipe at the top of the hand, near the index finger. Why? Well, the pinky, again, is the shortest finger, so it wouldn't be able to wrap around like the index finger can. So if you don't feel like re-drawing the fingers, start drawing the pipe from the bottom of the hand, and angle it so it fits in the hand correctly.

That's all I can think of for now. I hope it helps out some, I know I'm not that great with the tutorial things but I try at least. Email me any more questions you have about drawing hands and I'll try to come up with a better expanded version.