The essential idea is to focus on the subjugation of yuan shu mission after you've wrapped up the main storyline. Something that works really well is cranking up the difficulty to ultimate which becomes available once you finish the campaign. You'll want to gear up with that 30% proficiency boost equipment from the post-game merchant, and don't forget to grab some arborgreen consumables, they're seriously helpful for boosting your gains.

What makes this spot so good is how the troops keep respawning once you get into yuan shu's castle. The best farming spot is actually just northwest of where yuan shu hangs out, and you'll want to focus on those larger groups that keep showing up. Getting into a good rhythm with weapon combos and musou attacks is pretty important, since that's where the real proficiency gains come from.

You can easily rack up around 8 to 10 thousand weapon proficiency points in about 15 minutes, plus a bunch of skill points and some nice material drops. If you're specifically looking for gems, checking out the pyroxene spots that pop up in ji province while you're at it can be pretty worthwhile. Just remember to keep your starting horse handy, since you'll be doing a fair bit of running around between groups.

Good to know - using those arborgreen buffs right when you hit a big group can basically double your farming efficiency, so try to time those carefully.