In Runescape there is many ways to make gp. Most of them involve high stats. But in my guide I can help you make millions at any lvl wit most good money making skills. The first way is to get cow hides from cows of course which can be found near chickens in lumbridge. This is a starting way in f2p, mainly because cow hides are very easy to obtain and the sell for about 100 ea so 1k cow hides = 100kgp. The p2p way to start of is by picking flax and either making them into bowstring that sell for 150 or sell them as they are for 100 ea either way this is the best way to start.
Woodcutting
Woodcutting is a very good money making stat and is relatively easy but takes a long time. To start you need to cut regular trees and then oak until you get to willows this is where u can start making $$$. When you are at willows the best place to cut is south of draynor bank in f2p and also in p2p(mainly because there is no one there in p2p). it is best to cut like 10k and so that when sold you get 350k. I recommend to start cutting yew when you get to woodcutting lvl 70, that way it doesn't take you to long and when 1k yews are sold you can get like around 250k-300k.
Mining & Smithing
Mining and smithing like woodcutting takes very long but payout is good. To start get your mining lvl to the necessary lvl needed to mine iron ore. Once you got like 1k iron ore you can smelt or sell as it is either way it is good money. Also you can make steel bars provided that you got the lvl for it and sell bars for like 500 ea so 1k = 500kgp.
Fishing and Cooking
This the one of the most used method of making money in Runescape. To start you can fish shrimp right by the shore in draynor bank until you get high enough lvl to go fly fishing for salmon. Also cook all fish and shrimp caught so can cook lobster later on with out waiting to get your lvl up. Once to lvl 40 fishing and cooking it is now time for lobsters the most bought food in Runescape. Lobster sell for 200 ea raw and 250 ea cooked and you can sell to almost any one.
If I missed any thing or messed please feel free to leave a comment
P.S. I know fletching is not up here but I am working on a more detailed guide for that stat.