Let me begin with farther and further, since these were mentioned in a comment recently. I’ve struggled with these myself, but when I have trouble remembering something, I find that a gimmick works well for me.
Farther is used for distance, so I think of “far.“
Further is used for expanding on an idea, so I think of the word “furthermore.” You wouldn’t say “farthermore” so that narrows it right down.
Desert and dessert
I like to have my dessert in the desert. That’s all very fine, but how do I know which one has one “s” and which has two?
I think of a resort in a desert. Both words have one “s.”
Once I’m in the desert, I think of what a blessing it is to have a dessert there. Two “s”s in each of these words.
Ah, but there is trouble on the desert horizon. A disgruntled soldier is going to desert (pronounced like “dessert”). All I can think is that he is going to leave the resort (one “s”) and if he does that, he will NOT get dessert (two “s”s).
Bear and bare
For a start, my gimmick is for “bare,” and I think of part of the word (bare), because if you are bare, you ARE naked.
All the other meanings are spelled bear.
Bear is an animal. Bear means to carry or to withstand an ordeal. I imagine a big strong bear who can carry the load and put up with a lot. He can bear it. You can even have him marching along on two feet with a shotgun over his shoulder and a sign that says, “The 2nd amendment says we have the right to keep and arm bears.”
Stationary and stationery
These two words gave me trouble in elementary school already. I came up with a gimmick way back then and it has worked for me ever since.
The spelling difference is the “a” and the “e.”
Stationary means not moving from a place, so I think of the “a” for “at” a place. Stationery means letter-writing material, so I think of the “e” in “letter.”
I would bet that you have gimmicks that work for you. If you care to share them, please do. It might make someone else’s writing life easier.