Watch the Week 7: Foggy Mountain Special - Part 1 online guitar lesson by Roberto Dalla Vecchia from Flat Out Flatpicking
If you want to be a clean player, there's only one thing to do: practice slowly and work on polishing your tunes. Playing slowly allows you to "magnify" the weaknesses in your playing. Makes sure you hear every note clearly. No buzzes, mutes, or muffled notes. Practice using just enough pressure to get a clear sound. Once you really know "Foggy Mountain Special" and you've polished it, practice playing the tune from top to end without stopping. Don't let any mistake stop you, learning to recover from a mistake is a precious and valuable lesson.
Record yourself, and you'll notice things on the recording that you never noticed before. Don't worry, it's not all bad! Yes, there will be sections where you thought you were making the phrasing clear, but it just sounds blah. That's why you want to record yourself.