there are quite a few ways for f2p and p2p players to make fast money
mining: level 40 mine and sell gold ore (bars are worth less) level 55 mine and sell mithril ore (bars if you can smith them level 50 smithing required) level 70 mine and sell adanantite ore (bars worth more if you can smith) level 85 mine and sell runeite ore (runite ore found in wildernes level 47 and heroes' guild
hunting: level 1 hunt polar kibbits
woodcutting: level 60 cut yews in edgville and bank keep going till you have 1k yew logs then sell level 75 cut magic logs at the side of mage traning arena in al kahid
runecrafting: level 44 craft nature runes untill level 50 then do the great orb project minigame level 50 great orb project minigame level 91 craft multipul nature runes
fishing: level 40 fish lobsters and sell raw on grand exchange (dont sell good cooked) level 62 fish monkfish and sell on grand exchange level 76 fish and sell sharks This is a nice way if you have low combat. If your p2p fight Green Drags. You almoust 50k per trip if you keep bones and sell them. Another p2p offer is to Fight Aviansies. They drop adamantite bars noted 4 very common.
Then if your f2p i suggest u fight cockroach soldiers. They drop rune scimi's rune kiteshields and also alot of law runes.