When you know the purpose, you can then develop a structure or agenda to the rehearsal.
What will be the material you will work on?
What aspects of the material do you want to focus on?
How long do you want to spend on each item? What are the consequences if the goal for each item is not accomplished? Is this section a deal breaker for the tune or piece you are working on? Are there alternatives to the section that is giving you trouble? Is there more time before you need to present this publicly? Etc.
Be cognoscente of the amount of time you have to rehearse, and how long each item on your list will take. If you have 2 hours to rehearse, and you have 4 hours worth of material to work on, something has to go untouched for this rehearsal. Be aware if you know what you want to work on, you should be able to limit the amount of time spent on each task.
Also determine who is required for the rehearsal. There may be a dozen different things the rhythm section can work out without the leads that can take several hours or even multiple rehearsals. The sax player or horn section may only be needed for 7 out of 10 songs. If you are going to be working on the 3 they don't play on don't ask them to come to the rehearsal. Or if you are planning on working on 5 of the songs, including the 3 they don't play on, put the 2 they work on at the beginning of the rehearsal and send them home when they are done.
Also be sure to send the agenda/plan to the people attending the rehearsal ahead of time, so they have time to do thier homework.