For many people, overhead work tends to be quite difficult. If  you sit all day, your pecs and traps tend to become quite tight which can really limit your range of motion and make it hard to press overhead. 

Step 1: Release

Traps
 Pec major and minor
 Neck 
Lats


Stretch + Mobilize: 

Wall walks
Start with hand at hip height flat on the wall and walk your hand up overhead without shrugging 10x per side 2 sets

Wall Slides
Keep your bum against the wall, ensure no low back rounding, pull pelvis down. Start with forearms/hands flat on the wall at 90 degrees, slowly slide up overhead keeping core tight and midback engaged.

Strengthen: 

Banded Scapular movements.
Have a resistance band around wrists, forearms flat against the wall the whole time. Each movement will be performed on one side at a time. First movement is slide up 3 inches back to start point, slide out 2-3inches and back to starting position, out and slightly down 2-3 inches and back. Perform each movement 3 reps per movement per side, both sides 3 sets


Rotator cuff:
Keep elbows tucked in, rotate out slightly and back in. Very small movement, should feel burning in the shoulders.