Trading in EVE Online can be a lucrative profession if you're good at it. Here are some of the basic concepts that you will need to know as a trader.
Introduction to Trading
How do you do trading? First, buy something on the market. Then go someplace where you can sell it for more than you bought it.
This sounds simple, but to actually make good money from it takes skill (both in-game skill training as well as real-life skill), good equipment, and good knowledge of the market.
Make Money to Start Trading With
Before you can start buying things to trade, you will need some money. Go on missions for NPC agents, or do some mining, or whatever you're most comfortable with. It doesn't have to be a huge sum, as long as it's enough to let you buy enough of a trade good to start your trading career with.
Choosing What to Buy
Now that you have some money, you can buy things to trade. When looking for something on the market to trade, keep in mind that whatever you choose to trade, you will start by setting up a buy order for that item. To set up a good buy order, you will want to set the buy price to an amount higher than all of the other buy prices in that region. That way, you can be fairly sure that someone will sell their goods to you instead of to someone else.
But be careful to restrict the range when setting up the buy order. If you set the buy order to cover the entire region, then you might find yourself having to go all the way across the region, possibly through low-sec systems, to pick up what you bought. And when time is money, you will discover that long trips with an empty cargo hold are a big waste of money.
Before you buy, though, make sure that the goods are worth selling. The idea is to make a profit (even a small one) from the goods that you bought. This means that once you have spent the money to buy the goods, you need to earn more money per item when you sell them. You need to sell them for more than you spent on them, so look for an item on the market whose highest buy price is lower than the lowest sell price. That way, once you pick up the goods, you can create a sell order with a price lower than the lowest sell price, and since there are plenty of lazy players in EVE, you can be pretty sure that someone will buy your goods from you at that price.
Of course, you don't have to restrict your trading to one region. If you go around to different regions, you might find an even more favorable profit margin.
Time is Money
Another thing to keep in mind when trading is that time is money. If you find an item that you can make a ton of money on, but only if you travel for an hour to sell the goods, then the transit time effectively lowers the value of the goods. Think of it this way: if you calculate how many minutes (or seconds if you want to be more precise) it takes, between researching a trade good and selling it, and divide your profits by that number, you get the ISK per minute that you made on that trade. This is the true measure of the value of a trade. The profit isn't the only number you should pay attention to.
And if you can manage to consistently increase that number, you'll be well on your way to trading success.
Know the Market
To know the market means that you know how much a good is selling for, and how many buy/sell orders are being placed, and whether the prices are on a trend of becoming better or worse in terms of possible profit, and so on. The only way to gain this knowledge is by research and experience.
There are plenty of NPC corporations that consistently buy and sell various types of trade goods. Research to find out who buys and sells what. You might be able to shuttle goods back and forth between two corporations that buy and sell their respective goods.
Pay special attention to the number of orders placed each day by checking out the Price History tab in the market. Look for the option to view as a chart, and change the time span of the chart to the length of time that you're interested in (it goes up to a year). You will see how many buy and sell orders were created each day for that item. An item that has a large number of daily orders might have a lot of competition among traders, which will make it harder to make a profit on that item. Of course, if an item has almost no buy or sell orders most of the time, you probably can't make much (if any) money from trading it.
Being able to hold a huge number of items in your cargo space might increase your profit per unit of time. But be sure to keep in mind the speed of your ship: you might discover that even a small ship with small cargo space might make a bigger profit per unit of time than a huge industrial, simply because of the shorter transit time.
If your cargo space is empty after selling your trade goods, try to buy something else to trade as soon as possible. Flying around with an empty cargo hold is just wasting money.
Pirates are your enemy, and they're all over the place in low security systems. Even in high security systems, there are those who will destroy your ship and pod you. Monitor the routes that you take and make sure not to go through low security systems at all, if possible. Use your map and avoid systems where people have been podded recently, as well.