It can be difficult learning what is good to trade and when to know when you are looking at a really good buy or a really good sales opportunity. This comes with experience, but there is a tool available to help you learn and decide what those good deals are. Its called the Market Window, when you are looking at products, learn to use the detail view of the item. This will show you how much things are going to cost you and how much you can sell them for in the whole region. If an item is being sought or sold, it will show up on the detail. The way to read the detail is to look at the order details, look for the cheapest sell order for the product and make sure the item is NOT in lowsec if you are not comfortable. Now find the most expnsive buy order, also making sure it is not in lowsec. Very often the prices will be very close, but usually there will be enough of a gap to make a profit.
You have to decide whether that gap is big enough to justify making the trip or not. If you can make a deal, travel only 1 jump and profit 5 million dollars, that is probably an amazingly good deal, especially for new traders. If you have to travel through 15 jumps and you only profit 20,000 isk, although yes its a profit, it may not be worth your time. You also want to make sure that your taxes and broker's fees don't turn that 20,000 ISK gross profit into zero net profit. The fastest way to build capital (money), is to find the best deals that create the least amount of work. For instance, in my case, sometimes Jita will have a buy order which FAR exceeds the value of a local buy order for my product, and although I might make 20 millioin ISK more for a single deal, I probably will be forced to travel between 15 and 20 jumps to get to Jita. My frieghter takes nearly 1.5 hours to get to Jita from my area of operation. Then I have to return FROM jita, and that's another 1.5 hours. In that time, I can literally make 4 or 5 trips in my normal routes, and gross profit 40 million ISK each full route.
Was it worth chasing that extra 20 Million ISK? Most definately not, I probably lose between 150-250 million ISK worth of gross profit if I did that. Needless to say I have only made that longer trip two times with my freighter, and its not worth it. I lost money, and I was so bored that I fell asleep at the COMM several times that evening before docking somewhere and getting some shut-eye.