Convention yourself

If there's one thing you can do yourself a lot of fun with, it's conventions. Huh, conventions? Aren’t that these long and boring lists of things you need to comply with, from variable names to comment structure? Which you never ever seem to be able to adhere to in full? Yes, that’s what I mean!

There are two main reasons why conventions are important:

I admit, conventions have a bad name. Sometimes they’re used to wrap long red tapes around programming efforts, which reduces all the fun. But applied properly they can absolutely help improving the comprehensibility of the code. How can we make them effective?

With respect to comprehensibility, what are the basic things important enough to have a convention about?