How do you find a short in an 95 Chevrolet pick up that blows fuse for th tail lights and dash lights when you turn the lights on?

Try removing the tailight fixtures from the rear of the truck (GM had some problems with these) Replace fuse and see if it blows again. If so problem may be a dead short in the dash panel or in the switch itself. If it doesn't blow check and/or replace rear tailight fixtures