the absolute BEST (in my opinion) thing to use is PAINT TOOL SAI. it cost about 60 bucks, and you get a free thirty day trial. if you don't have the money, you can still draw the stuff in sai and then just copy the pictures to paint, and save it there (because after the 30 day trial you can't save on sai).
along with being AMAZINGLY SMOOTH with the tablet pen (unlike the free GIMP 2.6 program) it also includes the "smoother". this is something at the top of the program with the number 0
What this does is it SLOWS DOWN the tablet pen, and automatically makes your lines cleaner.
http://i1176.photobucket.com/albums/x330/obscenecupcakegifts/sai.png (See all the way on the right)
also, if you look all the way on the left, you will see a grey area. if you look closely there you will see a blank piece of paper with a pen on it. this is sai's version of the pen/path tool. It slows down your pen, like the smoother, but it also shows marks where the line changes direction, so you can change it that way. I don't use this often, sticking with the smoother, but it IS helpful, especially when drawing straight lines.
One more thing- I reccomend downloading SAI AND gimp 2.6
gimp is a free program that is very similar to photoshop. I reccomend you download this because with gimp you can add CUSTOMIZED BRUSHES to your picture, making EASY backgrounds.
here are tutorials on gimp http://browse.deviantart.com/?qh=§ion=&q=gimp+2.6+tutorial
here are tutorials on sai http://browse.deviantart.com/?qh=§ion=&q=tutorial+SAI
here are customized gimp brushes http://browse.deviantart.com/?qh=§ion=&q=gimp+brushes