Once you start getting the behavior and commands where they need to be
4- Start looking at groups in your area. Most places especially hospitals, nursing homes, etc aren't interested in a dog without an insurance policy. You get the insurance policy by joining a pet therapy group. Google "Pet Therapy" + the name of your city. Talk to vets or dog trainers in your area. Things to look for in a pet therapy group - size of the insurance policy. Where do they already visit. Notoriety (help you open doors to places they don't already visit) Membership fees (usually very minimal, especially considering the insurance policy you'll receive!). If they have a presence in your city I would strongly suggest Delta Society (www.deltasociety.org) or Therapy Dogs, Inc (www.therapydogs.com) They have a lot of notoriety and a large insurance policy.
5-Once you've decided which group to join, look at the requirements. Usually there will be an obedience test. They'll make sure your dog doesn't jump at loud noises or act uncomfortable or too interested in other dogs. They'll probably give his ear or paw a tug to see his reaction. The dog shouldn't nip or over-react to that. Then comes what I call the probation period. You'll have to pair up with a member and go on supervised visits. This usually is for at least 10 hours, of sessions no more than an hour long at a time. This may take awhile, but stick with it. I think Scrappy took a few months to get his 10 hours in. there may be one final obedience/temperment test and then if your dog passes - Congrats you made it!
Tips - before any visit or testing, walk your dog! For Scrappy before he 'goes to work' we make a trip to the dog park. I walk around 2x keeping him beside me then he gets free time. I call it getting his wiggles out. Then when we show up he's not all revved up about getting out of the house, he's already been out of the house for at least 40 minutes. He's also not all excited about seeing new dogs, he gets that out of his system at the dog park. If I'm short on time we just go for a brisk walk around the block at home.
I already said it but socialize like crazy. Get the dog used to new people, new sounds, new scents, new everything. He should take it in stride. Make sure he isn't jumpy about loud noises or sudden movement. What the person testing and supervising is looking for is this. The dog is eager to be pet, without being pushy. Scrappy walks towards people and pauses. Either they will reach out to touch or I'll call him away. If they reach out he'll go in for a closer snuggle. They don't want to see your dog lowering his head if someone reaches out, or rolling over.
Know your dogs limits. For instance, I know from experience some people that don't have a lot of control over their movement. One lady LOVES the dogs, she just beams when they come in but she shakes quite a bit. Some people don't visit with her, their dogs don't appreciate the occasional thump she might accidentally hand out. Scrappy sees her and starts wagging his whole tail so hard the whole back end goes to and fro. For whatever reason he understands, I just try and have her pet along his back so she isn't thumping his head. With kids Scrappy can get too revved up, I just excuse myself take him aside and calm him down again. When he starts to relax we go back to work. An hour is most dogs limit. After that they want a potty break, water and a nap

You'll be surprised how much visiting can wear you both out.
Be prepared! I wear a bag that is stocked with essentials and yes I have used everything I've packed in there. I keep poop bags on hand - thankfully Scrappy hasn't made this mistake yet but in the year I've been doing this I've seen 2 other dogs have an oops moment. Wet wipes - especially with kids who may have messy hands. A towel - good for wiping his feet off when we first go in. TREATS. Hand out liberally especially during your first few visits, make it an extremely positive experience. Vet records, when visiting places like a hospital they'll want to make a copy. And now I can carry his certification paperwork, and our official badges. Then a few other things I keep on hand for his circus tricks.