I know this is a Transformice forum, but I know some people out there will be interested in what I have to say.
Step 1: Build up your budget. Later on will involve taking your money and expanding it with the Grand Exchange, but first you need to get some initial money. I recommend mining a whole lot, then smithing steel bars. Each steel bar is worth 1000+ gp, which is a huge amount for just two coals and one iron ore.
Step 2: Find an object. This object can be anything, but don't choose something too small because it won't change value at all during one day, and don't choose something too big because you need to have a large quantity of that object. I will not disclose the object I use as I don't want any compitition.
Step 3: Buy that object at minimum price, or medium if you are brave. Then, put that item back on the market at one GP over the minimum (if you plan on not playing Runescape for awhile, sell it at mid-full price.)
Step 4: Wait, this step will be monotonous, but your item should sell overnight if you made a good choice. Also, while your item is on the market, work on gaining more money through mining and smithing.
1. The more money you start off with, the more money you will gain (duh.)
2. Try to make at least 1-2 percent gain from each object you sell. That way, you will improve your wealth by up to 5% every day. The next day you will get 5% of your original thing, plus 5% of the first 5%.
4. This is pretty much the only method to make GP by your self on Runescape without work.
5. Real-world trading is risky.
6. Don't be a fat lard and play Runescape all day. I am only on for an hour a day or so, yet I still get money from the Grand Exchange.
7. Before you advertise your wealth to your friends, make sure you have a very secure password. I've had at least one friend who decided to jack my account. Luckily I knew my recovery questions.
8. Have a nice day.
9. PLAY TRANSFORMICE. It is fun.