Buy quality, don't compromise.
Stick with the basics, until you decide you need more-
Don't buy a case trimmer, until you need one.
Don't worry about specialty dies (X-dies, collet dies, bushing dies, etc), until you understand basic dies.
Don't buy every
powder listed in your load data, but don't think you can use just one
Buy used, if you can find a good deal.
Don't believe anything on an internet forum.