If the fuse is good, I'd start at the battery and work my way towards the starter, checking for voltage. Go from the battery to the key switch to the safety switches to the starter solenoid to the starter. See where there is a break.
Also a simple thing to check is that the switch harness is fully inserted into the key switch. I've banged my head against a wall in the past only to discover the harness was slightly pulled out so the starter wouldn't crank.