If we speak about tips and tricks, be sure to try doing a maximal performance without any mask or goggles. It makes a great difference! Not only because of better hydrodynamics, but especially due to much stronger and quicker diving response. Well, in most pools it will be probably difficult to do the entire training without goggles, because your eyes may get irritated too much, but doing it once a time when trying a max perf will be no problem, and I am sure you will be able to improve your PB in this way. You may also wash your eyes with a physiological fluid after the training to avoid irritation. And do not be afraid, you'll see sufficiently well even without goggles.