Hi Ian,
The visual check for blown electrolytic capacitors is to check the top of the cylinder. It should be flat with an 'X' shape in it. When they go out, typically the top will be bulged up and sometimes the X will even open up.
Resistors are harder, as an ohmmeter is normally used to check them, but for a visual inspection you're looking for any signs of heat damage; typically discolored or blackened components on the board.