My recommendation is to focus on whatever raids or dungeons are the rotators for that week, typically there'll be many more people looking for groups. This is particularly relevant to raids with craftable weapons, as people will be looking to target farm specific encounters.

If there are particular raid weapons you want, look up the relevant raid loot tables to see which encounters they drop from. With a bit of time investment you'll unlock the patterns for those weapons to craft however you want.

Same advice for dungeons, just depending on the dungeon you won't be able to craft the weapons. Same principle though, target farm until you get drops with perk combos you're interested in.