My band has a strong guitar player and a young, inexperienced piano player. What strategies should I employ in rehearsal to balance the sound?
In contrast to the wind instrumentalists, whose parts dictate the exact intent of the arranger, rhythm section players must interpret their parts, based upon knowledge they have hopefully acquired and assimilated through hours of listening. One of our roles as educators is to steer and direct their listening habits. Some piano / guitar pairings which should be studied include:
Count Basie / Freddie Green, Wynton Kelly / Wes Montgomery, Lyle Mays / Pat Metheny, Chick Corea / Al Dimeola, Fred Hersch / Bill Frisell, Brad Mehldau / Pat Metheny.
How you handle the situation you have outlined above, will depend upon your specific goals. Do you need them to sound good FAST - for an upcoming concert or competition, or do you want to patiently nurture their skills and musicianship? Sometimes we are forced into taking the "quick fix" route because of deadlines or other circumstances. I admit to occasionally instructing the weaker rhythm section player to "turn down" or "play less". I have also written out specific chord voicings, rhythms and melodic lines for my pianists and guitarists to play. This helps to make the rhythm section sound more focused and less cluttered, but it doesn't really teach them skills which they can apply to future repertoire.
Ideally, every band room should have a library of instructional books and videos to teach genre specific skills for rhythm section instruments. Dozens of titles can be found at www.jazzbooks.com. Directors should also have stacks of CDs available. Recorded examples speak volumes more than verbal descriptions.
I accomplish the most with my rhythm sections during sectionals. If you can't arrange for an additional timeslot, I suggest occasionally breaking into sectionals during a regular rehearsal time. If you have good, welltrained section leaders, and provide them with a list of what passages to address, you might be amazed at how much gets done. During these breakout sessions, I spend most of my time with the rhythm section because their improvement has the greatest impact upon the entire band. Within your rhythm section sectional, play a recording and have the students identify and describe what they heard. Then have them try to replicate that sound, using the chord structure from one of their jazz ensemble charts or a fake book lead sheet. (If you can provide them with the exact chord changes from the recorded example -- even better.) With a young band, I will only choose repertoire for which I have recordings for them to listen, study and emulate.
By having them play as a unit without the horns, both you and they will know what needs to be addressed.