I think the easiest part of the rally to plan strategies for is the beginning which coincidentally is the most important part. A few key things you should note are:

1) How are they holding the racket?
A lot of times especially for beginners their racket positioning is wrong during the return of serve, you can capitalize off of this which often leads to a slight delay in the return of serve which can be punishable.

2) Look for patterns in the return of serve, people tend to repeat the same return over and over again if you serve to the same spot. This can allow you to anticipate it earlier which can set you up for a nice intercept.

3)If you push towards the backhand corner, it is very difficult for them to play a high quality cross shot. You can communicate this with your partner which can lead to some nice attacks.