Currently, the most recent advice relating swap AUs is featured in the Undertale Community, and is also made by @souptaels
However, I feel like as if the critics relating how to handle swap takes aren't exactly the most "helpful", so I felt like making my own version!
And as a special guest, I am bringing NotSoMania, the person who owns TFG!Deltaswap to help me explain a bit about how handling swap takes works and what to do with them

1. Swaps

Don't be afraid to do whatever swaps people already did, using the same swaps really won't affect how your AU is
All you really need to know is that making it similar to other AUs won't really help make your AU standout
Take TS!Underswap for example, instead of handling Sans as most swap AUs do (Him being basically just Papyrus), they handle him differently, that's a way of handling a swap as such
ALSO, don't be afraid to change swaps to your liking, either
You're obviously not FORCED to do that, but if you consider it fits well with your story rather than a swap that most people are doing, go for it

- Mania Note: Swapping personalities is kinda lame but 50/50 is interesting

2. Story

A key thing about Undertale in specific was its story, the it was handled, the characters, etc.
I think that's the most important aspect in an AU of any kind, swap AU or not
Having special mechanics and stuff like that will never be as important as the story, even if you add as many of them as possible

- Mania Note: It doesn't need to have special mechanics and shit, just a unique story

3. The "Ambitious" Issue

Posting your concepts and ideas relating swap takes is perfectly okay, no matter how many people complain about it
If I'm being honest, I think that's a better way of doing it than trying to turn a swap AU into something complete
Not saying that you can't do that, of course, but it's only going to drain you and demotivate you

- Mania Note: If you're gonna make it a thing my advice is to at least do it for fun and NOT because you want attention, because that's what literally 90% of the swap AUs do