What important differences are there between Tom and Huck in The Adventures of Huckleberry Finn?
Tom is an imaginative, rather impractical adventurer. He is well-read, and as a result often gets the two of them in a lot of trouble and mischief when it wasn't necessary. Take for example, the "rescue" of Jim. They could have gotten him out of the shed immediately, but because of Tom's insistence on making it like it is in the books that he has read, Jim has to stay for much longer, suffer quite a bit, and it ends up in Tom's injury. So, Tom is a much more adventurous type, in the sense that he likes to come up with games and schemes to entertain himself.
Huck on the other hand lives in a much more logical and practical manner. His entire life is an adventure--he doesn't need to make up schemes to stay busy and active. His father makes his life one big mysterious adventure. Huck is less "civilized" in the sense that he doesn't like school or reading, isn't educated like Tom, and so likes to be more free and unrestrained by society's customs. Tom comes from a more stable setting and is educated, so has to invent action for himself. Huck has a very practical head on his shoulders, and really thinks through the implications of his decisions. He plans smart rescues (like when he escaped his father), and reads people pretty well.
I hope that those thoughts helped; good luck!