that’s a big question! ask the developers if they have any standards on this first. The platform/engine may dictate some of this. There’s no hard and fast rule about SFX/UI or otherwise and headroom between music etc. It takes some iteration, that’s the name of the game. and the other name of the game is implementation, and if you are using middleware (fmod, wwise etc) you can tweak the knobs all day long until you’re happy. It’s always tough to bake in the right levels, but I still have to do it on some mobile games, and you just use your ears!