Get better Pokemon is the gist of it.
You may want to look up good mons for Tera Raids, but generally you'll want some Pokemon who can boost, heal, and do a bunch of damage, a good one being Iron Hands.
You can also get a good mon, do the raids you know you can win, and then reset your raids and keep doing the ones you know you can win, that's what I like doing. There are also certain raids that have a higher chance for more Herba, so look out for those (I forgot which, I know Cetitan is a good one).
This is the best advice I can give you since I haven't played Violet in a while, but good luck!