I didn’t really get a good idea of what level you’re at, so here’s a recipe for some simple hanging dust off the top of my head. If you’re looking for something more complicated get back to me.
Particular Dust
1. Make a really large emitter,, large enough to fill your screen.
2. Turn that velocity waaaaay down.
3. Go to the start of your timeline and turn the particles per second WAY up,, now keyframe that value.
4. Move forward one keyframe and set that particles per second to 0. This way you won’t have dust magically appearing throughout your piece,, iow the number of particles on the second frame will remain constant throughout. If you want more or less particles change the value on the first frame.
5. Turn the longevity of your particle up to match the length of your piece,, you don’t want your dust to disappear midway.
6. If you don’t feel like making your own particle texture I recommend using the smoklet or cloudlet at a very small size. I don’t like using the sphere cos it’s too round, dust isn’t perfectly round.
7. Mess around with the turbulence if you feel like it… but as it stand you should have some pretty decent looking dust going on.