Is there a known way to do it that gets the best results?

How bent we talking?  The structure was originally a circle.  A dent will mean it will be very hard to make it an even circle ever again.  You could try putting it into a vice and very gently tap the dent out again with a small punch or somethinglike that.  Do a little at a time.  Between each tap session put the spool in the reel and see how it rotates and fits.  You could chalk the opening on the non-drive side and see where the spool rubs (rubs off onto the spool).  I would also question how the balance of the spool would be (effect braking).  A dent essentially moves material from where it was when the spool was balanced. Even if you get it back to roundish it's not what it was.  If you know a machinist they could get it darn close but at $$$/hour.

Maybe the best solution is to replace it.  Also check with DVT. https://www.delawarevalleytackle.com/

Unless you have a lathe and measuring equipment it's junk, replace it.

Small edge of a baitcaster, middle of the spool, spinning reel?? Pic??

I don't have any bent spools at the moment, its just something i've had in the past, and i did find a good way to unbend the edge (on baitcasters) to its original form by using small metal scissors made to cut nails (yes!). You use the round handle portion, place the spool on a hard flat surface, and apply some pressure on the bent section with the scissors handle. It does the job well, but i was wondering if there's a better way, or maybe a tool made for the task.

Round nose pliers are best for repairing damaged spool lips.  You aren't going to get it perfectly round, but you can get it round enough that won't notice it unless you're looking for it.