In beginner and intermediate level tennis, serves typically angle naturally towards the outside corners of the service boxes.
Serves placed directly up the center towards the "T" are rare at these levels.
Also, serving speeds at these levels are relatively slow.
Unlike the pros on TV, recreational serves are usually under 50 miles per hour.
For the above reasons, the optimum receiving position for a service returner is right in the corner of the baseline and the singles sideline.
I coach my students to actually place one foot on the baseline and the other on the singles sideline. I also tell them to point their toes, their nose and their racket tip at the server.
This compromise position allows most players to effectively reach the vast majority of serves.
When advanced spin, placement and pace enter the picture, things change somewhat, but not as much as you might think.
As the match progresses and players learn each other’s styles and habits, the returning position can be adjusted. For example, certain servers routinely serve the same patterns over and over and over; they don’t vary their placements and so become very predictable. Make a note of that.
Try the "corner position" for yourself. It works. Adjust as you go.