First you need to find an organization to foster for. There may be a rescue group in your area desperate for fosters, or a shelter that is overflowing and needs fosters. When you look at the various organizations in your area, find out what the support is like for foster parents. Are dogs placed with foster parents and then forgotten about? Do they have numerous adoption events and a good website to help with placing your foster? Will you have any say in the adoption process? Will the organization foot medical bills? Will you get any supplies such as a crate or food? Will you get any help with behavioral issues that come up or will it be up to you to find a behaviorist? All of the above can influence which group you would like to foster for. If you can, talk to foster parents to find out the pros and cons of fostering for that group. I do find fostering enjoyable. So do my dogs. Though it is rewarding, you have to WORK for those rewards. You might get a dog that has no "issues" at all, but inevitably you will. Your job as a foster parent is to make the dog as highly adoptable as possible. For example, my own dog jumps up. If he were a foster I'd be much more strict about allowing absolutely NO jumping, because it could cost him a home. But he's already home so he gets to be spoiled a bit! Other dogs might be on the timid side. They might need help being housebroken or crate trained. They might pull a lot on leash and need training. They might need to be socialized in every way possible.

If you're a really busy person, I would advise against a puppy as you won't have time for him. Puppies take up a lot of time because you have to mold them into the right behaviors as they grow. What you probably should have is an adult dog. I'd recommend a low-energy breed that has already been housetrained and is friendly. Breeders sometimes have young adults for sale and then there are always rescues and shelters. If you decide to go with a breeder, make sure it is a reputable one.