First thing I always do is put a brand new glow plug in it and make sure my ignitor battery is fully charged. My rc8 is very termpermental with even slightly used glow plugs and sometimes won't start even if the glow plug appears to be glowing outside the engine just fine. Also check to make sure the carb is not loose and the idle screw is set with a gap of about 1 mm.

Edit: One more thing, make sure fuel is actually making it into the carb.