The hardest part about making your first million in Runescape is getting your first 100K. But if you follow this guide it will become very easy.
The best way for non-members that most people use is mining iron ore. Your going to need a bronze pickaxe to start off mining. There's a respawning one in the mining guild which is in Falador. There is an image showing where the mining guild is in Falador.
Go to the mining spot near the River Lum. There are three rocks there that you can mine tin ore from, although there might be some competition so even though tin ore is only worth around 28 GP you could sell some and then buy an iron pickaxe to defeat some of the competition.
If you have bought an iron pickaxe then you don't actually need the tin ore, so you should just drop the tin ore after mining it to raise your mining level quicker. Once you've reach level 15 you can head towards Falador to the mining spot across from clan camp. There are four iron rocks at the south-west of the mine. Mine there until you get your mining level up to 38 when you can mine coal in the barbarian village and sell it for around 232 GP. When your mining level is 40 you can mine gold in the same place you mined iron and you can sell the gold ore for around 213 GP. You can keep mining until you get your first 100K and then you can start merchanting.
Merchanting is basically the buying of something when its cheap and the selling of it when it's price rises. The Grand Exchange Database page on Runescape shows graphs of every item on Runescape so you know when to buy and when to sell. I will leave a link to the Grand Exchange Database in the Links section of the site. There are two ways to merchant.
1. Flip Merchanting works like this. Say you want to make money off Water Runes. What you do is, you type in "Water Runes" in the Grand Exchange Database. There you can see if it's rising or crashing. If it's crashing, do not touch it. If it's normal, rising a few hundred GP, use it. Now this is very simple. All you do is buy as much as you want, depending on the profit you want to make, for lower than market price. Not a lot lower just about 1-2 GP lower. Now wait for them to buy. Once they've bought sell them for the market price or 1 GP higher and you've made a profit. You should no that cheaper things will need to be bought in large quantities to made a good profit, whereas more expensive things can be bought in smaller quantities. Runes and Ranged items are good for Flip Merchanting.
2. Invest Merchanting works just how it sounds, you invest in an item, wait until it rises, then sell it. It's a very tricky, yet easy thing to do once you understand it. The Grand Exchange Database on the homepage is your best friend for merchanting. Always check the charts. It can show if the item is rising, or if it's going to crash soon. You have to learn how to read the graphs correctly. If the item is rising like mad, you should not buy it. The best items are the ones that are lower than they should be. Buy as many as you can, even if it keeps falling. It will always rise. Patience is the most important factor in making money out of Invest Merchanting, without it you'll just lose money.