Trading is a very profitable thing in EVE, however it takes money to make money.
Trading is also very redundant causing you to take the same route over and over.
What you want to look for in a route is an in system double trade route.
These routes are rare and are worth looking for.

Most of the time trade goods with high costs yield a better profit and are good for trade, but they take up more
of your cargo hold.
Trade routes in EVE due run out of demand, so here are a list of key things you need to know about trading in EVE.

First when you want to search for a trade route, you go into market option in a station.
Once you have opened that make sure to select the entire region of space your in.
This allows you to search all over the region for trade routes.
Now select an item of trade goods, once picking an item click on the green button under is image.
This brings up advanced market info.
You'll see the entire region and there will be two tabs, one says supply and one says demand.
Pretty self-explanatory and with those you can see where on the map systems that are buying and selling.

On the map you want to look for Green glowing lights on the systems, that means the price is good.
Red usually means that you don't even want to bother with it, but check anyway.
You check by sliding your mouse over the systems dot on the map,
if you hold your mouse there long enough it shows the systems name and price of the item and how much of it.
After flipping back and forth through the tab and you decide on a route my advice is to travel to the buy system.
Some times even when you click on the system and try to buy it from there it gets it somewhere else.

Now if you traveled to the system and it contains many systems what you do is pick one go to it and dock.
Once again pull up advanced market info but change your selection of region to system.
This will give you a map and will show you what stations are buying and selling.
It's a faster way then flying to all of the stations.

Some tips:

1. Make sure to check your cargo capacity and the density of the object you
only wanna buy what you can hold.

2. Always look for the double trade route.

3. If you plan on buying something keep trading till you have more then enough
to hold your trade goods, so you don't have to start from scratch again.

4. Be very weary of people in the system with you, they probably know what your
doing if it is a good run.

5. If you want to hold more cargo, cargo expanders do the trick, but you pay
for them with a slower ship.