So you've decided to build a new building. My first piece of advice would to to contact your local sector manager and ask what they suggest. Oftentimes they are more aware of shortages and over abundance than the average trader.
Once you have decided on a building type the next question is where. Consider which buildings are nearby that you can use to supply yours and which places are nearby that your building will supply. The shorter and more numerous the trade routes the more likely people will be to frequent your buildling. Also there are usual paths that people travel in each sector namely between starbases, planets and wormholes. These paths are often good places for buildings.
Another way to get increased visibility and trade is to list your building in the building sector index. Using the same wording as in the chat rooms (for example :ore: and :food:) you can make a quick readily available list that anyone in the sector can quickly access and see that your building is on their route and buying or selling at a good price.
The buildilng sector index is also a good place to see how much the competitors and other alliance mates are buying and selling at.
Pricing should be your next consideration. If you plan on supplying your own buildings then you can probably buy at lower prices, however if you want to make sure people come to your building and supply it regularly you may want to make sure they make a good profit.
The next step is dealing with production level and building size. Obviously the bigger the building the better off you are but upgrading size can be quite expensive. Using simple math you should be able to figure out how many tons of goods your building uses each cycle. Then figure out if it produces more or less than it uses. If it produces more make sure you have free space in your building to accept the goods or they will dump into space. If it produces less tonnage than it uses you can fill your building to the brim with supplies.
Another good practice is trying to stock your building with equal amounts of resources relative to it's usage and how often you plan on supplying it or getting it supplied. For example I try to keep 15 cycles of production in my radiation collector. It uses 3 food 8 energy and 3 water per cycle and produces 18 radiation. I try to keep my building stocked with 45 food 120 energy and 45 water. It uses 14 tons per cycle and produces 18 which is an extra 4 per cycle so I also keep 60 tons of open room in my building. This makes a minimum size for my buidling at 270.
Using simple math it is often very easy to figure out how much of everything you need to keep around. Using the max and min settings I keep the same resource ratio and try for a 3 production cycle minimum and 15 maximum that way no one comes along and sells me 200 tons of energy fills up my building and shuts it down costing me extra AP's to cart away the excess energy.
And remember if after all of this you still have questions or can't seem to figure something out Alliance chat is just a click away and me and your fellow guild mates will help in any way we can. Good luck and happy trading.