Start with clean, denatured alcohol. All work should be done outside, or in a *very* well-ventilated room. Use caution! - Avoid breathing the fumes as much as possible, and stay away from any open flame or spark source. You may wish to wear rubber gloves, but this is optional if you are just doing 1 or 2 boards. Find a shallow pan or dish (like an aluminum pie pan, for instance) large enough for your circuit board. Place the board in the pan and add enough alcohol to cover the board (you do not have to cover the components). You can let the board soak for a few minutes if you like. Take a medium-small paint brush with fairly soft bristles and work it over the board, dipping it in the alcohol as you go. The idea is to clean off all solder flux residue and any other dirt that may have built-up. Work the brush over the board and around the components until you are satisfied that it is clean. Dump the dirty alcohol and refill the bath with clean. Agitate the board a bit, and finally tip the board up on one edge and dribble a bit of clean alcohol over it to complete the process. Shake off the excess alcohol and leave the board out to dry completely. If you have a source of compressed air (or canned gas) use it to blow-out any sockets or complex parts. When you have completed this process properly, your board should be completely clean, and all solder joints should appear bright and shiny, and free of flux residue. If you find any really hard, stubborn deposits, you can work to remove them with a small tool like a dental pick (or something close). Regular denatured alcohol will not harm your components, but avoid any other solvents like acetone, MEK, etc.
