1. Learn to play your rolls with the proper emphasis on the accented beats of the music - This statement is really a mouthful because it is the essence of the banjo or any music. The most natural players fall on this without conceptualizing it, but I guess I must be more mechanical than natural. While sitting down with Mike Munford, there was a great difference in the sound and effect of him playing a forward roll on three open strings and when I played the same thing. I asked him why, and he responded with a question, Can you accent any note of the forward roll at any time? It was distressing to realize that I could not do that. Further discussion revealed that much of the drive in a banjo roll comes from a regular accent on the first and third beats of each measure (in 4/4 time). If you do the arithmetic, you will realize that a three finger roll requires you to rotate the accent from thumb to index to middle finger to achieve the accent on these beats. This was a profound revelation for me because it immediately changed the sound of many songs that I knew how to play and almost the forced the melody out of many Scruggs breaks. This concept applies to any roll, but you will understand why the forward roll is the staple of bluegrass when you hear this concept in action. Until you can get your rolls properly accented and in time, it will be very difficult or iineffective to do some of the syncopation that make some of the great players really exciting.
As Dan Mazer indicated, rolls must be second nature. Many banjo players seem to settle into a roll pattern that they can do without thinking (the forward roll, the forward backward roll, the backward roll, or the alternating thumb roll). To achieve drive and play the melody, you must be able to play your rolls unconsciously. For a beginning banjo player, it is important to spend a fair amount of your practice time getting your rolls smooth, properly accented and powerful.
2. Learn how to practice effectively - I attended Pete Wernick's banjo camp three years ago, and one of the lasting lessons of that experience was learning to practice effectively. I think many of us tend to practice entire breaks and gloss over the weak spots, figuring that they will get better eventually. Pete's approach is to isolate the trouble spots, convert them into a one to two measure phrase that can be repeated without stopping, and then practice them until you've got it. When you re-insert the trouble spot into the song, it will likely sound better than the rest of your break. This approach also works for memorizing breaks. I have used Pete's approach and it has resuscitated numerous breaks.
3. Practice with a rhythm device - The other big lesson I got out of Pete Wernick's banjo camp was the importance of practicing with a rhythm device. I had always been intimidated by metronomes, but had heard from many of the better musicians how useful they are. I bought a used drum machine, and practicing with it has really straightened out my timing. The discussion of rolls in Item 1 above is critical to do with a rhythm device. If you pursue this and are having trouble, contact me off list and I'll try to help you get going.
4. You're not going to play it well fast until you can play it well slowly - It is critical to play the right notes in the proper timing at a slow speed before you try to play a song up to the proper tempo. A rhythm device is also extremely helpful in regulating your speed; you can increase the tempo a little each day as you get comfortable with what you are trying to learn. Many beginning and intermediate banjo players think drive in banjo playing will be enhanced with speed; if you don't have drive in your playing at the slower tempos, you're not going to have it at the faster tempos.
5. Tablature and Traditional Notation - There has been much discussion over the years about the best way to learn banjo music. I think that all have useful characteristics and that the student needs to know how to read tablature and traditional notation, but should use them as tools rather than a crutch. Miles indicated that he is having trouble reading traditional notation. I think tablature is a more useful resource for understanding roll patterns/approaches and fingering, while traditional notation is very useful for understanding music theory. I played in a community theater production of The Robber Bridegroom about ten years ago and was handed a score of music for the banjo. I couldn't sort it out until I heard Tony Trischka's recorded versions from the off broadway production. The big bottom line for a bluegrass banjo player is that you have to train your ear, your brain, and your hands to execute.
I hope this advice is helpful to other banjo players on the list and can save you the time that it took me to finally come around. If I only knew then what I know now... Also, I know that there are many other aspects that can be discussed so I'll be interested in the comments of the many accomplished banjo players on this list to hear what has worked for them.