Go to the local library. There are usually a few books. A google search will give you some ideas for dead falls, etc... Be aware that most primitive traps are illegal to use.

Snares are the ideal for light weight, effective traps that are easy to set. If you are determined to go totally primitive then you are limiting yourself. You have to be proficient at making cordage from plant fibers at hand to make good snares. If you haven't done this much before, I'd encourage you to work your way into the medieval thing through several experiences. Utilize some technology to start. Many will find that even having a .22 and some cable snares could challenge them for survival. If you have snares you can probably live off of tree squirrels if they are plentiful and you know what you are doing...