Everyone wants to improve pitching velocity, but unfortunately, the answer to the question of "how" is different for everyone.  To that end, I pulled together a quick list of strategies you can use to improve pitching velocity.  They aren't the same for everyone, but chances are that at least a few of these will help you.  I'd encourage you to print this off and highlight the areas in which you think you can improve.

 Optimize mechanics (this could be 100 more ways in itself; I will leave it alone for now).

 Gain weight (if skinny).

 Lose weight (if fat).

 Get taller (shorter throwers can’t create as much separation, and are further away from homeplate)

 Get shorter (taller throwers have more energy leaks).

Long toss.

 Throw weighted baseballs.

 Throw underweighted balls.

 Improve thoracic spine mobility.

 Improve glenohumeral joint stability (rotator cuff strength and timing).

 Improve hip extension mobility

Activate the deep neck flexors.

 Extend your pre-game warm-up.

 Shorten your pre-game warm-up.

 Increase lower body strength.

 Speed up your tempo.

 Slow down your tempo.

 Get angrier.

 Get calmer.

 Get more aggressive with your leg kick.

 Get less aggressive with your leg kick.

 Don’t grip the ball as firm.

 Throw a 4-seam instead of a 2-seam.

 Get through the ball instead of around it.

 Improve balancing proficiency.

 Throw out all your participation trophies.

 Do more unilateral upper body training.

Recover better (shout-out to my buddy Lee Fiocchi’s Accelerated Arm Recovery DVD seton this front; it’s good stuff).

 Throw in warmer weather.

 Wear warmer clothing under your jersey.

 Change footwear (guys usually throw harder in cleats).

Throw less.

 Throw more.

 Pitch less.

 Pitch more.

 Politely ask your mom to stop yelling, “Super job, kiddo!” after every pitch you throw.

 Stop thinking that the exact workout a big league pitcher uses is exactly what you need to do.

 Subcategory of above: Remove the phrase "But Tim Lincecum does it" from your vocabulary. You aren't Tim Lincecum, and you probably never will be.  Heck, Tim Lincecum isn't Tim Lincecum anymore, either. You can learn from his delivery, but 99.9999% of people who try to copy his delivery fail miserably.

 Read more.  This applies to personal development in a general sense, and baseball is certainly no exception.  The guys who have the longest, most successful careers are usually the ones who dedicate themselves to learning about their craft.

 Stay away from alcohol.  It kills tissue quality, negatively affects protein synthesis, messes with sleep quality, and screws with hormonal status

.

 Incorporate more single-leg landings with your plyos; you land on one leg when you throw, don't you?

 Be a good teammate.  If you aren't a tool, they'll be more likely to help you when you get into a funk with your mechanics or need someone to light a fire under your butt.

 Respect the game.  Pitchers who don't respect the game invariably end up getting plunked the first time they wind up going up to bat.  Getting hit by a lot of pitches isn't going to help your velocity.

Throw a jacket on between innings to keep your body temperature up.

 Pitch from the wind-up.

 Drink magical velocity-increasing snake oil (just making sure you were still reading and paying attention).

 Pick a better walkout song.

 Get on a steeper mound (expect this to also increase arm stress).

 Train hip mobility and core stability simultaneously.