You just opened a can of worms. lol
If I had to pick one main piece of advice that I wish someone had told me before I started it would be......hmmmmmm
When you buy or add something to your set up make sure your buying what you want and it's the best you can get. It will save you from buying a ton of the same item just trying to decide if it's good enough. You can waste a lot of money that way. For example if you buying a new sight. Check them all out in person not in a magazine. Look through them and then decide. Don't just buy one cause it looks good. You'll just end up wanting something better.
That and practice religiously.