The way I started out was trading Runescape gp to CS:GO. I got around 250-300 keys to start with. I basically turned that to around 1700+ keys over a period of a few months. It's very time consuming, though. Essentially what I do is: I buy higher tier knives/skins with my keys at a price that I feel I can make profit from. I then sell the knife/skin for either more keys than I paid or I downgrade it into multiple knives/skins. I then sell them back into keys for more than what I started with. Rinse and repeat. You just have to learn the market. The supply and demand, etc.