I'd be a much better player today if I had started playing competitively much earlier. I was intimidated by the thought of playing in a tournament, figured a newcomer had no place in them. Sure wish I had.
I think many of you are correct in saying how important it is to learn the discs you are throwing inside and out. But I also think it is just as important to experiment with many different discs. I think every newcomer should go through the excitement of shopping the DG store to stock up their bag for the first time, and being excited about trying out that new driver. But, and this is a big but, learn your disc before moving on to the next one. Learn to throw them nose down and be able to manipulate the flight. Work the big spike hyzers to a certain distance, learn to throw a roller, practice forehand and backhand shots, thumbers and tommys, grenades and push anhyzers. Throw 'em slow, throw 'em fast, learn how they handle the wind. And then master your next disc.
We all know how much fun it is taking a bag out to the practice field, and unloading all your drivers as far as you can. Enjoy trying to throw for distance! But learn from your throws, and make corrections to your mechanics while you do it. And for every bag full you hurl, switch it up the next time and practice a different shot type.
And when you're done practicing driving, PULL OUT THOSE MIDS AND PUTTERS!!! Definitely don't neglect your slower discs, as the majority of the strokes in a round are thrown with mids and putters, no matter what course you're playing. Work some in the open field, learning the flight and spin, and then work around obstacles to a target. As you learn to manipulate the flight, you'll figure out body position, which helps your mechanics, which increases your distance.
And most importantly, get a practice basket and putt like crazy!