Recently, I’ve ended up needing to splice three strand, double braid, and hollow braid polypropylene ropes — though fortunately not to each other. While having the correct sizes and type of fids helps, it’s useful to have a guide to help navigate the complexities and ease frustration.
For the moment, the only tips I can offer is when splicing double braid, sweat the cover back over the splice using a hitch in a bungee cord (this saves your hands), also keep working the cover as you pull the core back through.
New England Ropes has a free handy Guide to Splicing that you can download.