I don’t think rules, as commonly formulated, are very useful in the context of Computing lessons. Rules are usually framed in the negative. For example, in a computer lab I went into a few years ago on one of my school visits, there was a poster on the door listing all the things that people shouldn’t do:

Do not leave the computers on.

Do not leave printing next to the computers.

Do not just switch the computers off.

and so on.

There are two main problems with this sort of thing.