helmets!
a good quality chain tool! (paired with regular chain replacement)
ask for a few opinions on set up from other riders, just cause your used to/adapted to it doesn't make it right or beneficial
solid parts not weight weenie parts, especially if you can't afford stuff often. theres no point having a scandalously light bike if its so delicate you can't push yourself on it.
Push yourself, often.
don't talk yourself out of things you dislike (techniques and moves, not lines that will kill you)
ride new places often, you'll wanna try things cause time isn't on your side like a home-ride.
Convince other, better, riders to ride your local spots, you might be humbled, but it's worth it to know what you can try/whats possible/new lines etc.
Learn to true wheels
Stay on top of your bike maintenance
Buy good tools.
Learn to do all your maintenance; you'll save, and even make some, money. you'll be able to solve/anticipate problems.
Carry enough spares; thats a tube, patches, and a chain, maybe even a set of brake pads.
if your riding a new place with no locals, do your homework before you go, find out if there is a high quality bike shop so you can get any 'unique' parts so you can keep on riding.
ride as many bikes as you can, get a feel for things that you like, avoid bikes that you can't afford or justify, you'll just be sad that you can't have them.
savage brakes, high EP freewheels are a must; they're not to expensive and the confidence they grant is worth it.
after that over size bars, aluminium forks and ISIS bottom bracket, then you know your bike is reliable...