Query Writing Best Practices

Hello all!

I'm looking to crowdsource best practices for query writing! I've done extensive research in the community blog posts and discussion threads and can't find more than a few basic and obvious tips and tricks...

This question is coming up because I inherited a relatively old app, that has slowly grown into a Frankenstein mess. It now has tables with hundreds of thousands, sometimes millions, of records with weird relationships. So, I have to turn to queries -- But my queries regularly get overridden by QB and stopped, or they try to run and slow down the whole realm. FTR, I don't have access to the performance optimizer.

Thanks!