The Point of Rehearsal
When performing scripted theatre, a lengthy rehearsal period is a given. The actors need to memorize and practice the lines. They work with the director on the staging, blocking, motivation, characters, etc. Over time, the properties, set, costumes, lights and sound are integrated until all the parts fit together. Once the show is running (with regular performances), there might be a brush-up rehearsal to tighten things up, adjust to a new venue or to serve as a refresher during a break. But, most of the time is spent on performing that tightly scripted piece.
What about unscripted theatre (i.e., improv)? There are no lines. The role of the coach / director is smaller; there might not even be one. There are hardly any properties, set pieces, costumes, lights and sound to consider. So, there's a natural inclination to skip straight to performance mode. It happens. New improv troupes do the minimum to gel and develop a format before going into performance mode. Specialty gimmick-based shows might only have one rehearsal before performance. Troupe members are more likely to miss rehearsal (low priority) than miss a performance. Since most improvisers are in it for stage time, these minimal-rehearsal approaches are tempting; however, the product suffers. The shows are mediocre and the audience primarily consists of the performers' friends. In our "everyone gets a trophy" society, you will get a lot of compliments, even for a mediocre show. Everyone wants to give you encouragement. Don't believe the hype. Unless you are turning people away from your performances, your show can be better. Even if your show is good, why not improve it? Your audience will notice.
The point of rehearsal is to craft a worthwhile product that appeals to the audience and makes full use of the ensemble.
Perhaps staged theatre is the wrong model. Consider professional football instead. At most (making it to the Super Bowl), a team has 19 meaningful games. Before each game, there are four to five practices. Before the season, there are pre-season games which don't count but are used to assemble a roster and figure out what works for that team. Training camp comes before then. That's 120 days of practice and that doesn't even cover all the individual workouts that athletes do to keep their bodies in shape. Conservatively that's eight practices for each performance. Of the American sports (football, baseball, basketball, hockey), professional football is the most profitable and features the least amount of games. It wins through quality rather than quantity. Improv troupes would do well to take a similar practice-centric quality-oriented, rather than a performance-centric quantity-oriented, approach. Rehearse to craft a competitive product that people really want to see and tell their friends about.
Craft a Unique Product
There are plenty of copycat troupes that simply try to replicate what the premier troupes in the area already provide. Why would an audience member want to see a ripoff when they can have the genuine artifact? Yet, I see it over and over again. Short form troupes in the same area all use the same games. Long form troupes just do a sloppy montage or Harold. Even if the quality is good, it feels recycled. Audience members love to see something new. So, aim to provide something that nobody else is providing. The improv space is vast; it is not that hard to find something new.
Don't Rush into Performance Mode
There's a real freedom to not having a performance on the schedule. Until you have a solid product to present, don't rush into performances. Figure it out in rehearsal! When you fail in a performance, that's bad. That audience is less inclined to see you again. When you fail in rehearsal, that's good. You've found something that you can work on. Use rehearsal to figure out what you are good at and what you are bad at. Exploit the former and work on the latter. Your improv ability is not fixed; you can improve with practice. Rehearsal is a safe space. Take chances. Learn from your failures. Worst case scenario: That's not part of your performance. Use rehearsals to grow as both an individual improviser and as an ensemble.
At some point, having a performance on the horizon is a good thing. It can serve as a forcing function to make decisions about the format. For many, it adds a sense of urgency to rehearsal. Ultimately, you want to put the work out there and get feedback from an actual audience.
Polish for Performance
Once you have a good format and your ensemble feels comfortable presenting it, polish it for the audience. How do you transition smoothly between scenes? What are you wearing? What does your stage picture (boxes, chairs, flats, etc.) look like? How can you make use of that particular performance space? Do light costumes (e.g., hat, scarf) or properties make sense for your format? Do you have a skilled person operating the lights? What can they do to make it more professional? Can they call scenes? Do you have a skilled person providing sound (musical accompaniment, sound effects)? How can they more tightly integrate with the show / ensemble? At minimum, do you have entrance / curtain music? If there's a projector, could you benefit from some AV (e.g., put up your logo, backgrounds)? The audience appreciates such small touches of professionalism. They will appreciate the effort you put into the show.
Continue to Grow
Improv is a creative endeavor. Specific performance formats will grow stale over time. Performers get complacent. Audiences become bored. Let rehearsal be the "canary in the coal mine." If rehearsal is boring or not taken seriously, it is not a sign that you don't need to rehearse. It is a sign that you need to work on something new. Work on new games or a new format. You can roll out changes slowly or premier a new format (audiences love that). A great improv troupe as any great creative artist has to change over time.