Plan, Plan, Plan
Seriously, you can't be too prepared if you intend to do it yourself. Read and understand pool school, have a good test kit, watch MANY online pool install videos and make a comprehensive list on what you need. When it's time, you just execute the plan.
My thoughts:
- go as big as you can afford or have room for
- I recommend resin over steel
- if I did it again I'd upgrade every item in the "pool accessory kit" (ie: ladder, solar cover, pole, vacuum head, etc as most of these are sufficiently cheap as they will likely get re-purchased shortly after)
- anticipate a dedicate electrical circuit to your pool, have it adequately powered
- plan the area around the pool: decking, etc