Rehearsal is where the magic is created and perfected. If you are just going to be playing with a bunch of friends you’ll need to agree on the songs you are going to play, if it’s covers (covers are always a great place to start). If you are just starting out pick say 4 or 5 numbers, fairly straight forward ones (you can leave the complicated Genesis and Yes tracks until the second rehearsal). If you pick too many numbers to begin with you may find you turn up to rehearsal and you’ve all picked different songs and then you are a bit stuck and end up wasting a lot of time. Once you have picked your 4 or 5 songs decide on the key you are going to learn them in and which version you are going to learn, just make sure you are all learning from the same recordings. You may need to change the key of the songs if the current key is too high or low for your singer.
You’ll need a place to rehearse, if you are just going for an acoustic duo set, then anywhere without distractions will do (living room, kitchen, or even bathroom as the acoustic sounds may be better in there). If you are adding in drums and loud amplifiers and you don’t want to disturb the neighbours you’ll need a rehearsal room. There are lots of places set up for band rehearsals with PA and amps so you’ll just need to bring your guitars and maybe snare drum and cymbals. I’d always advise taking your own microphones as your singer(s) may not want to be tasting the slobber from the lead singer previous band while trying to sing. A quick web search should provide you with a list of local rehearsal studios. Obviously check price per hour, what you need to bring, where you will be parking (is it secure or in a dodgy part of town).
There are other alternatives, there may be a local church hall or some pubs/bars may have back rooms which you can hire. The big problem with these is that you will have to take all of your equipment with you including PA, drum kit, amplifiers , kettle, heaters, etc plus you will lose quite a lot of time in setting up, stripping down, loading and unloading your vehicles, and think of the strain on your back. A lot of musicians do end up with bad backs (and I am included in that statistic).
The best plan I’ve always found is to try and have your own rehearsal room, I’ve rehearsed in barns on farms, caravans, lock ups, store rooms, shops (we used to rehearse in my Dad’s record store on a Sunday morning), it’s best if you can find a place that you can leave your gear set up that you can lock up and secure. If you can keep a cheap/spare PA and amps set up in this space you won’t even have to strip down the room whenever you have a gig.
Also, I would definitely invest in some a handy recording device to record your rehearsals, back in the old days it was a portable tape recorder, and all the issues arising with using cassette tape. I now use a Zoom H2 Handy Recorder, there are plenty of others out there in the market, but I’m very happy with my H2. Digital technology is so much easier to work with than tape. Gete everyone in the band to listen back to the rehearsal recordings, this is where you see where you may be going wrong, or right, see what you need to work on. Also, it’s really handy if you are just jamming and maybe songwriting. Something played in the heat of rehearsal can be easily forgotten and lost to the world forever, and it just may have been the greatest song ever written.
Once you have the music down and tight, start thinking about stage craft, if you want to put some fancy dance moves into your show work out the choreography well in advance, and make sure you can actually still play your instrument and not crash into the drummer while doing that backflip.
Remember also that you will never be perfect, but don’t let that deter you from getting out there and gigging. Too many bands live in the rehearsal room, that’s fine if gigging is not your aim. Me personally, I just want to play live, and one gig is worth ten rehearsals, there is nothing like playing live, the rush you can get, the more you play live the more confident you get. So get out there and just do it. If you make a mistake, it doesn’t matter. I’ve had what amounts to car crashes on stage, where things had been so bad we’ve just had to stop the song altogether. If that happens just make a joke of it and move on. Also, if you make a mistake but you’ve managed to get through the number (or even if you haven’t) never apologise, most of the audience probably won’t have noticed anyway.
The old adage of the guitarist who makes a mistake in his solo, purposely makes the same mistake the next time round, so everyone then thinks he meant to do that in the first place. Entertainment is all smoke and mirrors anyway. Even the worst gig experiences are a learning experience. I once saw a guy come out of a particularly terrible gig saying “well that’s taught me a lesson”. Even the top pros make mistakes they just know how to cover them better than us mere mortals.