The Trick?? Well, there is no trick, it takes "practice"....with a little help from good genetics
I have been 6'1" since my junior year in high school. Back then, I could only jump to touch about an inch or so below the rim. To dunk a basketball, you need to be able to effectively get at least your wrist to be able to get to rim level, not your fingertips. where are you at now? can you at least touch rim?
Well, I can dunk now, pretty good too as I can do 1 hand, 2 hand, 2 hand reverse dunks, and even a "bootleg" double pump dunk. My secret to getting there? Squats, and lots of them.
I never trained legs up until my freshman year in college. After about 4 months of painful squats supersetted with heavy leg presses, I was dunking easy. Plyometrics help as well, box jumps or even something as simple as jump roping.
"practice" dunking while you're shooting around. Start out just inside the 3-point arc, take a couple hard dribbles to the rim and try as hard as you can to dunk. you'll only be doing layups, but if you attack the rim like you're going to dunk over and over again you'll build up your jump reflex. eventually you'll be getting your hand close to the rim and soon after above it.
You are 6'3" and based on your weight in good shape. I would say if you can't touch the base of the backboard by doing a vertical jump standing under it (no running start) you've got a long way to go. as the stallion said, not everyone is meant to, but you can sure as hell try
And if you need motivation, just look at this pic and listen to R. Kelly's "I believe I can Fly"