After making sure your battery is good, the next step is to check all the fuses. Notice I said all the fuses, not just the ones involved in the circuit that's having a fault. On more than one occasion, I’ve found a good fuse for the affected electrical system I'm trying to repair, and another fuse that seemed unrelated that was blown, which was the problem all along. It's worth checking all the fuses if you have an electrical failure. Nothing is more frustrating than tearing an entire vehicle apart looking for a problem in a wiring harness only to find that it was a blown fuse the whole time.
Lastly, don't forget about the large fuses that might be physically attached to the fuse box. Say you have a no-start condition, perhaps after attempting to jumpstart the vehicle. If the cables get hooked up wrong, it will normally blow one of these main fuses. So if you have a vehicle with no electrical power at all and a good battery, check the main fuses. You might find one that's blown.