Homebrew PCBs

Bare copper boards?

Scotchbrite first. You can get it in various grits (McMaster): I 
would use a fine one.
Then wipe on a coat of flux.
Then solder.

If you want, you can put a drop of solder on the tip of the iron and 
drag it along the traces. That will tin them nicely.

Flux remover after the soldering is done for a better appearance. Be 
careful with it around mechanical components like switches and 
relays. If the flux gets inside them it is hard to get out. (Ask me how I know.)