I don't think Martin touched off enough in
his guide so I'm writing my own. I'm also guessing since that the Runescape toolbar is official, it can go without an approval.
Requirements
-Patience, it can be very hard to pick up at first.
-Starting money. Between 100k - 1 million is a good amount.
-The ability to follow prices and price trends. Don't invest in a failing item.
Useful Tools
The Official Runescape Grand Exchange Price List
The Official Runescape Toolbar, it has a nifty feature that updates your browser on your GE item statuses, letting you do something else while having an up-to-date status checker.
An Intro to Flipping/Short Term Investments
Investments in the Grand Exchange can make you a serious amount of coins, in a seriously small matter of time. I make 1 - 5 mil an hour at mediocre skill levels using these techniques explained in this guide, and so, here's what you need to know.
What are these terms?
These terms can mean many different things to certain merchanters.
In my guide, short term investments are when investments in the Grand Exchange are used to amass a 1 - 10% profit in a matter of time longer than 30 minutes. Flipping is buying an item and selling it for 0.1 - 5% higher within 1 - 10 minutes.
Why should I invest?
Because, believe or not, the people you see with rares and uber loot, work for their money, be it investing, skilling or killing. Investing requires little skill requirements, and a base amount of money. So easy to do when you pick it up, too. Even F2P can join in on the fun. To make money post-Grand Exchange, you will usually need to use the GE. So why not use it to buy low and sell high and make a spare million too?
Short Term Investments
With short term investments, you're investing in a 30 minute - 4 hour period. You'll be investing most, if not all of your starting money. And when investing, bulk invest, bulk invest, bulk invest, buy cheap items. I can't stress it enough. This means, if you have 100k, you'd invest in 200 - 400 coin items, and sell them back for more. Look at my suggestions of items to bulk invest in at the bottom of my post. To start out, always check prices and trends before investing. Then, determine trial and error with single-item purchases to determine what people are actually selling for. Better to have lost 30 gp on a single lobster than 100k on a whole lot of them. Very few people actually sell/buy at the extremes.
Here's a small marginal investment to look at.
Say I have 450k and invest in 25k rune essence. I pay 18 coins an essence, then immediately post the 25k essence back at 19 coins an essence. I come back in a half an hour, and I find out I gained 475k coins. A 25k profit for no work? This is small investing, too, not even a 1% investment.
So how can I make lots of money?
The key is
profit per hour. If you're not making so much and your items are getting sold fast, consider flipping. Aim for 5 - 10% when short term investing. If you can move a 10% profit on a return, you are godlike at this. Even 5% is a lot on a return.
Flipping
In flipping, you'll be investing in a matter of 1 to 5 minutes. To flip, you don't need to know market trends as much, as a 5 minute investment won't crash as likely as an hour long one would. You need to trial and error to find the actual buying and selling points of an item you're selling. No, you will not make a 10% profit on a flip, it is almost impossible, and if you do, exploit it while you can, but don't expect too much.
When you've found the buying/selling points, buy the item as low as possible, then sell the item as high as possible. If you have to wait an extra 30 seconds for an extra 10k profit, so be it, as long as it's worth the wait, but investing in low price items is the safest way to flip. If you're not making 1% profit on an item anymore,
move on. It might not be worth your time.
Items to Invest
Credit given to Runescape Wikia for most of these, I personally don't flip these, but these are known to flip well. Choose a stable item out of these suggestions when investing.
-Arrows (Steel, Mithril, Rune)
-Throwing Knives (Bronze, Iron, Rune)
-Darts (Bronze, Iron, Dragon)
-Logs (Normal, Maple, Yews, Magic)
-Hides (Yak, Snake, Green dragonhide, Red dragonhide)
-Potions (Strength (3), Super Strength (3), Super Defence (3), Super Restore (3,4), Prayer (3))
-Runes (Air, Water, Nature, Dust, Cosmic, Laws, Deaths, Bloods, Chaos)
-Pure/Rune Essence
-Seeds (Harralander, Ranarr, Snapdragon, Limpwurt, Watermelon)
-Herbs (Harralander, Kwuarm, Ranarr, Lantadyme, Snapdragon)
-Bars (Iron, Steel, Silver, Gold, Mithril)
-Pouches (Yaks, Badgers, Ibis, Titans)
-Summoning Ingredients (Marigold, Red Spider Eggs, Raw Bird Meat)
-Keys (Brass, Loop Half, Tooth Half, Crystal Key, Sinister Key)
-Raws (Raw Tuna, Raw Lobster, Raw Swordfish, Raw Shark)
-Food (Lobsters, Swordfish, Tomatoes, Tuna, Tuna Potatoes, Monkfish, Shark, Pizzas)
Closing Words
I give credit to my friends for teaching me how to flip in the first place, and to Runescape Wikia for items to flip.
If you'd like to see a guide on anything other than merchanting, request it with a post or PM.