Music is a business. You have to decide how seriously you want to pursue your personal enjoyment versus making money. This is not to say that you can't have both and sometimes if you plan carefully you can have a rewarding experience in every way.
Many of you have played music on different levels and it's good to talk to other musicians to get ideas and learn from their experience. Some musicians are happy to rehearse together only, some are happy to do cover songs and others write and play original content and go for the big time. No matter what you decide, the planning of your endeavor is a most often ignored and important part of your success.
GOALS AND TIMELINES
Too many bands (especially those with younger members) just jam and let things fall into place. Sometimes it works, sometimes it doesn't. I would suggest that after you have your band together, you sit down and make a plan. No one likes band meetings unless they are productive. Every group has leaders and followers. Good leaders get the followers to contribute. You should also set one of every ten or so rehearsals aside, put the instruments down and update your plan.
These are some suggestions for some goals and timelines. I am basing this on a part-time band with three nights of rehearsal set aside until the band gets playing and then one night a week thereafter. You should pick your rehearsal nights and stick with them. Family and full-time jobs come first so you may have to make a few adjustments along the way. This is no way an excuse for bowling, golf, or other things that could have been scheduled around rehearsal.
Each rehearsal should last about four hours. The last part of rehearsal should be devoted to distributing the music to learn for the next rehearsal. Select one or two band members to make CD's or send files via the internet so everyone has the songs. This means that before you start, everyone did their homework they received from the rehearsal before. There is nothing more frustrating than watching someone fumble over their parts when you spent hours at home trying to learn the songs. This is critical and can ruin your plan and keep the band in the basement or garage forever. If someone is repeatedly unprepared, say adios.
Let's now assume you have to learn 40 songs to play a 4 show gig (some styles of music and venues would be much less so adjust these numbers accordingly). Let's also assume you can learn 4 songs per night with a variance for more or less difficult songs. At 3 rehearsals per week, that's 20 rehearsals so plan on 4 weeks to give you room to review and cancellations. This is an ambitious plan but it can be done. Try to select some of the easier songs to get rolling. Give yourself another 2 weeks to play the songs over again and maybe weed out some stinkers and learn some new ones. After your first week of rehearsal start booking your first gig and target it about 6 weeks from that date. It will give you something to shoot for and you have already created some "insurance time" just in case. The first gig does not have to be at on the Tonight Show or the Grand Ole' Opry. Someone's back yard or roof will do just fine - just play.
Everyone should have a song list and do not have a lot of dead air in between songs. Have a few beverages and update your plan at the next rehearsal night after the gig. If you can find an honest agent who will not sit back and collect from gigs you could have promoted on your own, then hook up with one. If possible, go for a while promoting your own gigs. There is plenty if internet out there and a web site, links, myspace, and word of mouth can go a long way.
If you build it - they will come.