What are tips to avoid sunburn if you burn very easily?

I burn really easily.

Even just walking around on a sunny day for a little over 30 minutes and I am noticeably pink after.

I want to be able to go to the beach and have fun, but I’m always afraid of burning. Since I had a bad experience with a burn 2 years back.

That time I reapplied sunscreen every hour and my sunblock was over 50 and waterproof.

I still got burned.

We were there the whole day from 10–6.
I had breaks under the tent too. While eating or resting, but I’m sure it only helped a bit.
It’s probably the single day in an entire year I ever get so much exposure.

Would I be able to prepare my body by giving it more exposure than I normally do? Gradually increasing it, so it’s not so bad when I actually go to the beach.

I don’t think it was ever this bad when I was still in school. I used to play tennis for practice and was often in the sun, so I only got burned if I didn’t protect myself.

But now I work all day and play tennis at night.

So what can I do to have a blast at the beach, while not paying for it the next two weeks?