A solid strength and conditioning program that adds velocity should include start with foam rolling and a dynamic warmup. This will promote blood flow and improve mobility.
After that, strength training is a great way to become a better athlete and add velocity.
Compound exercises (certain squat, deadlift, lunge variations) are great ways for a pitcher to add velocity. Core stability exercises such as planks, deadbugs, stability ball rollouts, TRX fallouts, etc. are great ways to work and stabilize the core. This is crucial to development.
Medicine ball work is another essential component to a solid program. Throwing medicine balls helps generate rotational power. This helps transfer force from lower body up the kinetic chain to the arm.
Arm care exercises are very important as well. Very light (2.5 lbs or less) arm care exercises such as Y's and T's are just two exercises aimed at keeping the arm healthy.