[pllbnk]

On the back-end application level programming side:

* Look for O(N^X), that is nested loops even when they are not necessarily expressed as loops on the language level.

* If possible, get rid of ORMs in favor of raw SQL. Not because ORMs are very bad but because almost nobody bothers to learn them; they often start causing issues with any non-trivial amount of load.

* Study data access patterns and figure out where and what composite indexes might help. I am saying composite indexes because I assume regular indexes are more or less always there, often even too many of them.

Especially with the last one I have achieved impressive results without any kind of impressive effort, just setting aside some time to understand the code.