This question should be answered before building your fence. You should be aware of the boundaries of your property. You do not want to get into a dispute with your neighbor because the fence is three or four inches into their property. You do not want to be responsible for a feud that is as bad as the Hatfield’s and the McCoy’s.
Another adverse consequence is that after building the darn thing, you will have to tear up all the work that you have done, due to the fence being on your neighbor's property. You should draw a line that is distinctive for you to read and this line does not fall into the next door neighbor's property. You should be aware of local zoning laws. Local zoning laws could be concerned with the height, width and length of the fence. If your property is a corner lot, you should make sure that you don't blind cars with your fence.
Also be aware of where the tree roots are on your property. You do not want to be that person who has to put a fence post through a tree root. Only Superman or Hercules will be able to put a fence post through a tree root. You will have to find those roots and dig to get to them. You will then have to cut them so you can put a fence post where you want it to be. It is not an easy task to get rid of the offending roots, but you will have to deal with the tree roots if you want to put the foot posts where you want them to be.
Where should I put my fence? You should put your fence within the boundaries of your property without violating local zoning laws or your next neighbor's property. You should not make sure that the fence posts will not be going through tree roots. These answers should make it easier to locate a place for your fence.