Few more thoughts from me:

* Don't treat your test code as second class citizen. For tests follow the same clean code principles you are following for your app code.

* I saw many dirty workarounds for selenium tests that didn't behave as expected. In major count of it happens due to lack of understanding selenium / test framework API. So read the docs. If something doesn't work - read the docs again ;)

* Don't test everything with selenium E2E tests. Test this way just most crucial scenarios. Leave more detailed stuff to unit tests.