I use Hazel’s “App Sweep” feature that will offer to trash related files when you trash an app (and will offer to put them back if you reinstall the app.
Beyond that, I tend not to worry too much about stuff that is left over on my Mac after I remove an app. If I see a large folder in ~/Library/ for an app that I no longer use, I can usually find out in a quick Google if it is safe to remove.