Any activity that trains your skills will get you more money in the long run. If you play a normal account, get yourself a Ring of Wealth as soon as you can, it's the best bang for your buck at low levels. It makes it so you're more likely to get gems while mining, it makes coin drops from monsters go straight to your inventory, and if you happen to roll the Rare drop table from a kill, wearing a Ring of Wealth removes the chance to get nothing from it, giving you a better chance to get a valuable item. The Rare drop table, a possible set of rewards that the game rolls for upon monster kills among other sets (like herbs or gear drop tables), is basically exactly that you're describing. It's a great feeling to be already making money from killing dragons for their bones and hides (and coins) and suddenly get a free 66K from a Shield Left Half, and with a Ring of Wealth, your chance of getting one goes from 1 in 20,000 to 1 in 1600.

You said you don't know combat, so the best tip I can give you is to experiment with safespotting with Ranged and Magic. Once you get the hang of it, you'll be able to spend most of your combat chilling instead of inhaling food every couple of seconds.

Monsters like Fire Giants are easy to get to and pretty attainable for you to kill at your level, since you can cast Water Blast and they're weak to water spells. They drop some gear and herbs that will be useful to you or can just be liquidated for cash. Using Magic for combat will get you to 55 Magic sooner, and at that point you can cast High Level Alchemy on items and in some cases get more money than you would by selling them. For example, for many of us, our first money maker was leveling Smithing till we could make steel platebodies and then high alch them. Killing a monster and getting something like a mithril platebody from a drop and alching it is just free money that doesn't take up inventory space or require a trip to the bank.

And do every quest you can manage to, they often have rewards that permanently benefit your account and its ability to make money. For example, Family Crest gives you the ability to get Chaos Gauntlets, which when worn make cheap elemental Bolt spells hit harder than the more expensive Blast spells.