All About Polyurethane

Don't...

Shake the can.
Shaking creates bubbles, which leave a rough, pitted surface. It's okay to shake wipe-on polys, however.

Thin the first coat.
Thinning doesn't improve adhesion, and you'll have to apply more coats and use more solvent.

Use tack cloths.
Some contain chemicals that prevent good adhesion.

Wax the finish.
Wax isn't durable and will interfere with any subsequent coats.