after reaming the hub (if needed), place the prop on a balancer, find the heavy blade (assuming your using a 2 bladed prop). Scrape the FRONT side of the heavy blade, altering the back will affect the props pitch. Try not to remove anything from the blade tip or the trailing edge, you could but there already fairly thin.

Also removing material from the hub weakens it, so I'd advise not to remove any material from here.

If its a wood prop don't forget to "finish it" I apply a dab of thin ca and spread it with my finger (wearing a latex glove, or plastic wrap of course!!!) This will seal the bare wood from oil, water...

I'm sure someone has some better tips but this should get ya started.

One more thing.. some people like to add paint or adhesive to the light side instead of sanding or scraping the heavy side. This is fine, except over time what ever you applied for weight may wear off, so check the balance often.

Good luck.