I usually burn very easily. I never go cheap on the sun block, i also always buy the highest spf i can find and apply it generously. Also for it to be effective it needs to be rubbed in. If it stays white on the surface of your skin it wont work, you skin needs to absorbe it. Not staying in the sun so long also helps..
I am fortunate in that I have hardly ever burned - though there has been some redness for a day or two. The one time I did burn slightly was as a 10 year old in Bulgaria at the height of summer (in the mid 60's) when suncream was barely thought about (no wasn't a nudist then!).
Since then, I have been careful with moderate suncreams/oils (generally 8-15 spf) starting with the higher factors for the initial days and using lower factors later in the holiday and go home with that even tan without the "white bits" We also go for lunch at the beach bar (which is shaded with matting) for a leisurely time at the hottest part of the day. Most folk do wear something at the beach bar such as a thong, swimwear, sarong, pareo or T-shirt and shorts even though the beach is 100% nudist just a few steps away which is slightly odd.
MOH is more sensitive to the sun and has higher factors and stays in the shade over most of the day