How to troubleshoot an engine that won't start in an Audi 80?

I have an Audi 80 that won't start and I suspect it's an engine problem. I want to know how to properly diagnose and troubleshoot this issue.

Check if there is enough fuel in the tank, if not, refuel and try starting again. If that doesn't work, check the battery connections and try jump starting the car. In some cases, faulty spark plugs can also cause the engine to not start.

Start by checking the fuel pump and fuel filter. If they are working fine, move on to checking the ignition system and the starter motor. The issue could also be with the engine sensors or the timing belt.