Honestly--and I'm saying this as someone who bathes dogs for a living--it's going to be much better if you let someone else do it.
Trying to bathe a large, shedding dog in your bathroom is back-breaking and messy; dog water and hair goes flying all over the place and it's really hard to clean up. It's also really hard to get your dog dry, especially in cooler weather--if your dog has a very thick coat, it can take days, and it's not good for their skin to be wet for that long.
A groomer has equipment set up to bathe and throughly dry that dog within a couple of hours. You pick up the dog, it's done, there is no cleanup on your end, and the result will be worlds better than what you can do at home. Your dog will look like a million bucks, and you only spent $50 or whatever. Well worth it, IMO.
If I didn't have access to a grooming shop, there's no way I would try to bathe my GSD at home. As a matter of fact, there was about a year where I didn't have a grooming shop and I *did* take my GSD to a groomer. She was great, my dog looked amazing, and I didn't have to get wet and hairy.