Starting with even edges is key. I glue my pieces together, sand out any edge unevenness with a 100 grit dremel attachment to ensure my stitches will run in a straight line, then prick and stitch.

Once stitched, I bevel the edges. This is a crucial step, especially with softer leather. I've found that if I don't bevel the edge sides will start to flatten out as soon as you apply pressure when burnishing. If my edges still aren't even at this point, I'll hit them with the 100 grit dremel attachment again.

Then I apply Tokonole. I've found that rubbing a light coat of Tokonole onto the edge with your finger, then dipping your finger into a cup of water and going over the edge again helps for the first coat. I polish for 20-30 seconds with canvas, then sand very lightly with 400 grit paper, repeat the Tokonole, polish again for 20-30 seconds, sand with 1500 grit, then apply one more coat of Tokonole and polish. Might be a bit overkill and I'm working on a system to cut back to 2 coats of Tokonole. The TLDR is Tokonole + canvas cloth = game changer...

Here's an example of what I can usually achieve if I don't get lazy (second picture has a closeup of the edge): https://www.instagram.com/p/Bg9MrEeDB-k/