Don't take an 8 to 10-year layoff from when you discover the sport and when you really start to play it. If I'd been playing ever since I found the sport in my early twenties, instead of forgetting it and waiting until age 30 to pick it back up, I might be a lot better by now.
Other than that, I don't have any other regrets. A few of the things I'm really glad I did early on that I'd recommend to others:
Learn to throw the disc low and flat (keep the nose down) early in your learning curve.
Be willing to ask lots of questions. Not all the experts are friendly, but many of them are, especially on this site. There's nothing like picking a friendly master's brain.
Become familiar with the sport's jargon, especially terms for the ways discs can fly. Then apply that knowledge to your disc selection. The second worst mistake most newbies make (after throwing those distance killing nose-up sky hyzers) is to be ignorant of the differences between their discs. Just like there's a difference between woods and irons and wedges and putters in ball golf, every disc is made for a different purpose.
If you don't know what the discs in your bag are for or what they do, go the manufacturers' websites and do a little homework. Then learn to play with your "beginner friendly" discs. If you don't have any beginner-friendly discs, the folks here will be more than happy to recommend a few. There are some real winners out there.
Lastly, and most importantly, remember always to have fun. That's the whole reason the sport was invented.