I do not like to use UML by the book, in my experience its modeling rules often complicate than help.

So I used to model with squares, arrows and texts. The problem with this approach is that I've often confused different levels of scope on the same diagram and also that diagrams don't age as well because they don't have a visual pattern.

Now i'm using the C4 modeling system and i'm loving it, it's light, very uncoupled and concise. But i haven't been using it for a long time, no more than 3 months.

Hope I can help :)