Groups of all kinds can benefit from deliberate practice just as individuals do. The idea is the same: find the trouble spots and work on them; spend your time working on the 10% that’s not smooth rather than the 90% that already makes you feel good.
Select a reference source. Don’t wait until everybody gets together to find out you all used a different version. Ensure that everybody has a copy or access to the reference.
Know your part. In most cases, you should know in advance what you’ll work on as a group. If individuals don’t know what they’re supposed to be doing separately, it will only be worse collectively.
Try to get questions answered beforehand if it’s possible. Some things have to be worked out as a group, of course, but not everything. Remember that if you have a question about what you’re supposed to do, somebody else probably has the same issue and they might not have run into it yet.
Listening is as important to a group as it is to an individual. Many mistakenly believe that a practice session should consist almost entirely of playing. Instead there should be a lot of time spent coordinating, handling the rough spots, deciding how to best put the parts together.
When listening as a group, listen and don’t play. Maybe you know your part but somebody else has questions about theirs and they can’t hear if you’re playing.
Use a DAW to record the songs if at all possible, it makes it easier to locate places of interest. This doesn’t have to record everything; you need to stop and playback for review.
However, be sure to record the entire session so any decisions are saved and everybody has the same reference material. This doesn’t require a DAW, any recording device is adequate.
Identify Problem Areas
Individuals can play against the reference to find problems but generally groups won’t do that. If you’re playing along with the original, though, be sure to play quietly enough to hear it.
Typically, groups will listen to their own efforts to find the trouble spots. Eventually your own version should become the reference.
Make Exercises Around the Problem Areas
For the most part, playing the trouble spots slower and at a lower volume than normal will be the best exercise. If the group can’t play something slowly, it will only be worse at speed.
It might happen that some members can’t play their part at speed. That’s fine; it should then become their task to be able to do that before the next group practice. In that case, when that spot can be played cleanly, move on to the next regardless of the speed you can actually play at. Only go as fast as the slowest can go while playing together.
As with individual practice, don’t play the whole song! Record the section you just worked on and listen to it again. You might have fixed one thing only to find that there was another that was hidden by the initial problem.
Group practice has all the problems of individual practice, compounded by any number of things. But the overall practice method should be the same: find out where you’re having trouble and work it out.