What I learned from having shoulder impingement in both of my shoulders at the same time:
1) Face Pulls: Probably one of the best things you can do for your shoulders. A great exercise for strengthening both your rear delts and the external rotators of your shoulder. It also works very well for rehabbing and prehabbing your shoulders.
2) Rows: Add some form of row to every session and match or exceed the pressing volume with your rows. I went from doing only Pendlay rows and bent over rows once or twice per week to rowing at least 6 times per week (out of 4 sessions per week). Not only is it bringing up my neglected back, but it's making it more natural for me to keep my back in a powerful position while pressing.
3) Dynamic stretching: Between every set of pressing movements (overhead, on a bench, with dumbbells or a barbell, doesn't matter), I do either band pull-aparts, or shoulder dislocates, sometimes both. Both of these help both loosen up a tight shoulder, stretch the pecs, and promote retracted scapulas.
This all has shown me that the shoulder (at least mine) responds well to high frequency training / rehabbing. In the case of only rehabbing exercises, since the intensity will be very low, it should be safe do them at the beginning or end of most or all of your training sessions.