There are a whole bunch of tutorials for papercraft, here are some good ones: http://www.papercraftmuseum.com/beginner-tutorial/http://www.papercraftmuseum.com/advanced-tutorial/
The most important thing about papercraft is having good glue
. I strongly suggest using Aleene's Tacky Glue
, it's the best glue I tested so far! It dries quickly, holds strong, doesn't make the paper wet and doesn't make annoying threads (less messy overall). Strong paper is also a good thing so it is less likely that the paper model collapses (but I have just been making these from regular A4 printer paper). You can also use rulers to make clean folds and use tweezers if something is too small to hold in your hands.