If tracks have only one direction, the wisest thing is to put one-directional signals on entrance tracks and nothing on exiting tracks.
If you don’t put any signal, one train can reserve the whole track including the crossing and prevent another train to even get near the crossing. If you put signals and the crossing is occupied, at least another train can approach the crossing just up to the point just before the crossing.
If tracks are bidirectional, things get more complicated. What I do is to put some buffers just before the crossing so that trains are never in the way of one another.
For example, in this picture, there is a one-directional track going from NE to SW, thus a signal at the entrance only. There is also a bidirectional track going from NW to SE (or the opposite). In this case, two buffers for trains to give way if another train goes in the same bidirectional track:
