So I am super short and poor so I usually have to hem my own pants. My mom taught me the official way to do it, but I am lazy and short on time. This is what I came up with.
First wash the pants at least 3 times and dry or you will end up with capris.
Second, turn them inside-out and put them on. Have someone else fold them OR fold them, look in a mirror and also try sitting down to make sure they are the right length for your preference. Make sure you are wearing the shoes.
Third, pin them in place. One or two pins in each leg is usually good enough if they aren't too baggy. Fold them first by holding the sides so the crease is along the seams and lay them on a large table or ironing board. Check the length to make sure they match. Then fold them so the crease is along the front and back and make sure they match that way.
Then iron the crease where the bottom of the hem will be. If you are shortening them more than two to three inches you may want to cut them to make sewing easier. If not, I leave it alone. You can always rip the stitches out and make them longer.
Then pick out a color of thread that is either closely matching or a good compliment (i.e. some jeans use a gold colored thread). If you are sloppy like me, choose a matching color so it won't be noticeable. ;) Sew on the machine.
Enjoy your handy work!