How to troubleshoot engine starting issues in Audi A2?

I have a 2004 Audi A2 and my engine won't start. I've checked the battery and it seems fine. What other things should I check to figure out the issue?

First, check if the fuel pump is working properly. If it is, then check the ignition system for any faults. If both of these are fine, then it might be an issue with the spark plugs or the engine control unit.

Make sure that the immobilizer is not activated. If it is, try using the spare key to see if the issue is resolved. If not, then it might be a problem with the starter motor or the electrical connections.