This fellow who signs himself "baseball guru" says he's 5'10" and weighs 140 pounds, is a lefty, his average speed is 75 mph but needs to be stronger and faster. Well, I never was a rip-roarin' fireballer myself, but I can offer a couple of suggestions as to what "baseball guru" can do.
First, guru, you need to put on twenty or twenty-five pounds---you are at the moment decidedly underweight, and the extra pounds should help. Second, I don't know how much throwing you do---and I mean just throwing, rather than pitching---but you need to do a lot of that. Many pitching coaches advocate throwing every day, because in doing this you will build up your arm strength. Third, you need to get your entire body into the action; a lot of pitchers make the mistake of throwing with just the arm and the shoulder, and that actually makes for a lot of home runs and other extra-base hits because the batters' attention is all on the upper half of the body in their quest for the pitch they can blast out of the ballpark, across the street, into Aunt Minnie's kitchen window and smack into the roast turkey on the table! They never stop to think that the real key to a pitcher's power is below the waist---the use of the legs and the hips to generate that power. I call this use of the entire body "The Secret", which I learned long ago from watching how the Yankees' Big Three pitchers did it.
Just my 75 cents' worth---rampant inflation, you know. 8)