[dsraven]

vent hose should end higher than the tank so, worst case scenario, no siphon effect can happen. I try to end the hose as high as possible
hose should be run with a smooth uphill flow, held with clamps along the route as required
a vent cap, like a differential would have, should be used on the final end to keep dust etc out
I always try to end the hose behind something so road splash doesn't have a chance to plug it. sometimes on the rear of a cross member or back along the tank filler hose so it vents near the filler, which is usually substancially higher than the tank. sometimes I will also run the diff vent hose along with it since it also needs to be placed somewhere with the same thought process
shield the hose from heat where applicable
also install a ground wire from the filler cap to the tank to stop static charge when filling. since the filler is insulated from the tank it's important