1. Practice drawing hands from live references
The nice thing about hands (and arms and legs): They're the only parts of your own body you can clearly see without a mirror. I often spend a few minutes sketching my own hand when I'm waiting for a class to start. It's good practice, and it helps avoid a. boredom b. noticing too much that the student directly behind and to the left of me is using the seat in front of him as a footrest, and isn't wearing shoes, and stockinged stranger feet are less than a yard away from my person and social conventions prevent me from doing anything about the nasty feet nasty gross-*
Perhaps you are thinking 'practice is a tip that took you all of ten seconds to think of' or 'I already knew practice leads to improvement' or 'I have art I need to post right now, and the hands look awful.' Okay, so, first off, they look more awful to you than to anyone else, because when you see your own art you're comparing it to an ideal image in your head. An outside viewer hasn't seen your picture anywhere else (unless you stole it, and in that case this post won't help you) and doesn't know if it fell short of what you were trying to create. So it's not as bad as you think. Second:
2. Basic construction of a hand
If you draw a lot, I'm sure you already have a method for building the hand, but everyone has slightly different ways of constructing things. I always find it helpful to see how someone else does it, whether I want to
Hands are CONSTANTLY changing shape, which is a big part of why they're so hard. I use different construction shapes for them depending on what they're doing. Like so:
A special note on fists: It is easier to draw a fist with the fingers wrapped around the thumb, because what is the DEAL with thumbs. However, if you punch something or someone with your thumb inside your fist, you run a risk of breaking your thumb. A character who is experienced at punching would know this. A n00b character might not know it, and you can torture said character by making them punch the wrong way and break their thumb. Wait, I meant to say that a character who fights a lot has more credibility if drawn with the thumb outside the fist.
3. Some ways to stylize hands
There are infinite ways to do it and you'll probably invent your own if you draw enough. Here are just a few examples for the curious. I invented none of them.
Power Glove. Now, that would be an interesting thing to put in a character design...
The middle and ring fingers are often kept next to each other and used as if they're one finger, particularly in Disney movies. It's a way to keep some of the simplification of a four-fingered hand without drawing something as cartoony as a four-fingered hand.
Oh, and fingernails are often ommitted. I... never draw fingernails.
When the wrist is straight, this is all you see.
Back-and-forth, the wrist has about 180 degrees of motion. I tried turning my wrist to the side and it kept stopping at seemingly random places, so I'll leave that for other artists to figure out.
Well, I'm nearing my 1,000-word limit and I think this is the end of what I actually know about drawing hands as opposed to what I think sounds plausible about drawing hands, so I'll leave you with this cool image I accidentally found when I was looking up references- oh, and here's a real tutorial by a more experienced artist.
* I know what you're thinking. 'Sketch the feet!' No. No. No. No. No. Well- no.