Haven't done any tips in a while, so...

Here's one way of making bezels fit to curved surfaces - such as large cabochons onto cuff bracelets, for example.

When making up the bezel, I tend to install a heftier piece of metal than normal for the bezel shelf. I do this primarily to support the structure of the bezel during the subsequent filing. The shelf needs to support the stone clear of the surface, so make sure there's plenty of depth to it - you can take it away easily, adding it back is trickier.

I invariably file a rough curve into the bottom of the besel at this point.

Using engineer's marking (not layout) blue - or Prussian blue oil paint, it's got a fair few similarities - I put a thin smear across the curved surface, then touch the bezel to it. Where the metals contact, there will be a blue mark left on the bezel. File it away... Repeat this until the entire bottom of the bezel shows blue and you will have a perfect fit.

Then clean it all up. The blue does like to get everywhere!