Hooo boy, there is a ton about Zard, but I'll try and and get just the important stuff.
First of all, Nair in pretty much undisputedly your best move. It's a great disjoint, has crazy priority, is a great spacing move, and has tons of possibilities for combos and mixups. Learn to use it often, one of Zard's favorite places to be relative to his opponent is to have his back facing them, so a quick jump Nair can catch pretty much anything. Learning how to Reverse Aerial Rush can be helpful if you have a more aggressive style.
Jab is another move that is incredibly useful, since it's really fast, is one of his many launchers, is also hugely disjointed, and is a great anti air if anyone is trying to SHFFL towards you (or combos but that's situation specific).
As far as throws are concerned, use Dthrow if you are looking for tech chases (not the most reliable but with quick reactions it is very hard to escape). You will probably want to regrab in most cases, or jab if you can read a neutral or no tech to start a combo. If you want raw percent and easier combos (and also tech chases at low percents) then use Bthrow. Without proper DI, it combos pretty regularly into Fair and much else besides.
Zard's recovery is also pretty dang good as well. Down b is awesome for horizontal recovery, and can be canceled into up b which has pretty good vertical recovery. Also glide-air has pretty huge priority and is useful if someone is trying to challenge your recover without disjoints.
Now, there is one combo that is considered to be your bread and butter against pretty much every character. If you ever manage to get an up-smash, up-tilt, or just any move that puts you on the ground and your opponent in the air directly above you, immediately Down B and charge fly. Use it to chase your opponent, chaining Uairs until you run out of jumps then finish with an up B. This combo will kill almost every character at medium percents on almost every stage, learn it and use it whenever you get the chance.
I'm pretty sure that I'm missing a few things, but I hope this covers the basics, also don't forget to check out videos of some of the top Zard players, I'll link a few below but feel free to explore some by yourself.
Happy Zarding!
Metroid:
GF - vs Vista (Falcon)
vs Darkatma (Marth)
Yomi:
http://www.youtube.com/watch?v=B4esgT4xkyQ
http://www.youtube.com/watch?v=QoBJS007U-w