In my opinion, the biggest factor for a dull blade early for a beginner is too steep a blade angle. The spine of the razor maybe too far away from your skin creating a scraping situation, rather than a slicing one.

I would put say 10laps in on the diamond spray, and see how that goes. If an improvement, do 10 more.

As to shaving, err on the low side - spine too close to the skin. Start with the gap between the spine and skin roughly equal to just over one spine width. Starting with your side burns slowly adjust the angle a little feeling for the sweet spot.

You may also be using too much pressure. Hold the blade loosely, but securely. Aim to be just scraping off the lather.

Hope that helps.