add water to the mud. I don't know how many people I see mudding walls and end up sanding the absolute heck out of it cause they can't get a smooth finish or it bubbles.
Drywall mud is water soluble.. add water, mix it up till you get the consistency your comfortable with using and away you go..
and another trick, before it's fully dry (give it about 1/2 hour to 45 minutes), use a damp sponge to feather it out.. if you practice you will never sand it again.