Find the tag and place it in the bottom right corner, and make sure that it's at the bottom of the sheet. Once the tag is in the correct location, the other corners will be easy peasy.
Or put it at the opposite corner!(Usually lower right/top left, but different brands locate their tags in different places.) Unless it's a directional floral, it will look the same and you'll get more even wear. Always start with the corner that's hardest to get at, and tuck it far under, so as you pull towards the others it will stay tucked.
I used to have this problem. I got some clips for the sheets and it stopped happening. So if this happens to you and you are annoyed by it you can consider getting some. They are called something like "sheet fasteners" or something
I can’t recommend these clips enough. I roll a lot in my sleep, and my fitted sheet used to ride up every night. I installed these clips and the sheet has not budged since.
Why not just do the prosleeper thing, and use the fitted sheet like a sleeping bag? Let the elastic bits cocoon you snugly by pulling the left and right sides over each other. You could put the pillow outside of the cocoon, and have the elastic bit on your neck if you like a little scratch on it at night, but I prefer the pillow to be pulled lightly into the back of my head for ultimate sheet snuggles.
I gave up on fitted sheets. I sleep with 1 corner untucked fitted sheet the entire time. If I fix it it's just going to come out next time I move. I don't care enough to try to staple it to my bed or something.