The first advice you need is that water quality is everything to these little guys. Buy a good test kit (not strips - the API Freshwater kit is often recommended) so you can keep a close eye on readings of ammonia, nitrites and nitrates (the first two should read zero, the nitrates 20-40). This is the most important thing you can do.
Other tips include correct temperature (must be no higher than 20 celcius, and try to keep it fairly stable), not too much bright light (they need hides to shelter from the light) and not too much of a current (they don't like it, so baffle outlets or direct them against the glass to minimise water disturbance). Earthworms are the most nutritious food for adult axies (or as soon as they can manage them really).
Finally, do NOT put anything in the tank that is smaller than the axie's head. Seriously. It will probably end up inside them, which is no fun for you or the lotl. Pebbles are a disaster. For youngsters, a bare-bottom tank is safest, as even sand can be ingested and cause nasty compactions in babies.
The advice on this site is second to none. Ask here before you go to your LFS (local fish shop), where staff may seem knowledgeable but often give downright dangerous information. Axolotls ARE NOT FISH so do not assume fish-shop staff know about axolotls. The people on this site do. They are your best source of help.
You will adore your lotl. Weird little creatures that they are, they will steal your heart (and hours of your time, watching their antics). Best of luck!