No I'm not ragging on new players I'm giving ways of making money.
There are many ways of making money but here are the easiest ways of making money from the best to worst.
1) Mining and smithing - Mine tin and copper until you have 56 of each. then take 14 tin and 14 copper with you to a furnace and smelt them to make a bronze bar. Go to the nearest anvil and make daggers until you can make scimitars. Sell the scimitars to Zeke in al-kharid and repeat until you can make plate legs. Make plate legs until you can make plate bodies and sell all the things you make.
2) Crafting - The most variable skill indeed. Start by mining clay and use a jug on a water source and use the jug on the clay. Use the softened clay on a pottery wheel (Barbarian Village) and repeat this process until you can make leather boots. Alternatively, you can kill cows and get their hide and take it to the tannery and get it tanned so you can make leather gloves. you can make much more money out of this.
3) Woodcutting - Cut down normal logs until you can cut down oaks. Sell all the logs that you obtain by woodcutting. You will make a fair amount of money out of this.
4) Combat - This would have to be the most popular skill. You can kill things all around RuneScape and get money from them. I recommend starting on goblins as they drop goblin mail which you can sell to the general stores for 48gp each. Keep on doing this until you get to level 15 combat. At level 15 combat, go fight Al-Kharid Warriors as they drop a nice loot. Continue to fight them until you get to level 30 combat. While at level 30 combat you are able to kill guards. So go do it. You should make a fair bit of money out of this.
5) Cooking - start cooking shrimps until you can cook anchovies. Cook anchovies until you can cook pies. Keep cooking until the next levels.
6) Fishing - The slowest way of making money. Fish for shrimp until you can fish for sardines. Fish for sardines until you can fish for herring. In that case, keep fishing the same way. When you can, start net fishing for anchovies as these will make you a bit of money.