Steps for performance tuning/debugging

There are many scenarios which could occur and the solution will be different for each of them. So rather than making things too complicated , I am looking for key steps which we can suggest to a developer to make their life easier in finding and fixing real issues rather than guiding them to follow more bookies' stuff. What should those steps be?

Something comes to mind like:-
Understanding the execution plan.
After that with gather_plan_statistics hint, finding the estimated cardinality vs actual cardinality and lookout for major deviation. Which would then point to the fixing the statistics of specific objects or higher dynamic sampling etc.

Anything else we can add or If you can guide me to any such blogs or already available Document, would be helpful?