The number one aspect to wheel truing and the one which is most overlooked by a newbie is spoke tension. Getting a wheel laterally true (side to side) is easy, radially true (up and down) a bit tougher and spoke tension a bit of an art and science combined. If your wheel looks fine but the tension is off, a couple of rides will render it really whacked out. Ideally you'd want to use a tensionmeter, but plucking the spokes to determine relative tension is ok in a pinch. You can true a wheel on the bike fine, though a stand is preferred. Poke around the net, far better instructions than I can give here. Just take your time, go gradually and eventually you'll get the hang of it.