Begin correct form push ups (set a goal of 100 per day after 2-4 weeks depending on overall fitness/strength, 3/4 days per week/ some do everyday. Start with 5 or 10 at a time if you have too, until you can manage 15/20 , then 5 or 7 sets of 20 or 15's spread throughout the entire day, whatever gets to your 100 total for the day) . Check out ytube for correct way to do pushups - from the tricep and chest ( Correct push up(https://www.youtube.com/watch?v=IODxDxX7oi4) and Shoulders with no weights(https://www.youtube.com/watch?v=BpbZC_Pd4XU)), doing this way will also activate/ strengthen and define the deltoids. . It's what i have been doing since the holocough began. Buy a pull up bar that can be fixed to door frames - front pull-ups are fantastic for deltoids with no free weights. Or do as my flatmate use too - Stand at full attention -- maintain absolute strict form -- and masturbate furiously 6-10 times a day.