There are three ways to make money on Runescape. The first is skilling. Getting high skills and using those skills to make money. Wood cutting, fishing and mining are just some off them.
Wood cutting
If you want to make money using wood cutting then I would suggest getting level 65, so that you will be able to cut yews a bit faster. Yews sell for about 400-500 sometimes.
Fishing
The only problem with fishing is that all the locations on F2P are no where near a bank. If you want to make big bucks then get level 55 so you can get swordfish a bit faster. Swordfish sell for about 450-510.
Mining