Two ways I know...

First, you can buy a silver pen to redraw the broken or missing traces on your board wherever they are broke. Pen uses Silver ink: conducts electricity. Make sure that the areas you are connecting are clean first. These pens are available at stores like radio Shak or any good electronics parts stores. MCM electronics or Parts Express are good sources for much cheaper than average stores.

Secondly, if you have a terriably oakward situation where you cannot draw in a new trace, you can drill a really small holes in two areas you are trying to bridge. Clean the areas and then solder in a small wire into those holes to bridge the failed connection.

Remember that the source of several other problems could be a trace that has lifted off your board under another grouded instrument. These are really hard to find, and relatively common. They can be glued down with a good super-glue and then bridged.

Hope this helps...

ATLD