Is it your intent to fish only salt or do you consider rivers an option? The reason I ask is because the two different areas of expertise require diverse knowledge.
I haven't guided salt but as Bob suggests you'll have to learn the area well before you'ld be of much use. Mostly because you don't get the same indication of the bottom and it's structure by just looking at the surface water the way you can on a river. This situation is slightly different on moving water. If you do a lot of river fishing and have operated a boat on rivers you probably can fish most any piece of water, and have somewhat of an understanding of where the fish are or should be holding. Combined with the fact the fish migrate to the rivers makes guiding rivers a little easier IMHO.
I used to guide the Alagnak (Branch) river outside King Salmon/Dillingham Alaska. While I wasn't the most knowledable of the holes on the river I did understand how to read the water. This translated into near instant fishing success for the salmon and trout runs (what else is ther?).
Another thing that will help a first timer is to find out who the lodge owner is. Call them, tell them that your interested in guiding and above all when you get one that agrees to meet you, pack all your confidence up in yourself and take it with you. They'll usually ask, "what makes you think you can guide a river". My response was a little cocky but it landed me the job, "I know I can. I have exceptional people skills. I understand rivers, and I can show people a good time while fishing too. What would make you think I can't." I brought an asortment of rigs I'd tied, and flies, which were effective for the area I would be fishing. I studied the runs so that I knew the different seasons. A little research goes a long way. But the bottom line is, if you don't have boat knowledge, and/or fishing knowledge you're starting off at a deficit. You'll need to get that skill somewhere and a couple years as camp help will go a ways to getting you there as suggested earlier.
Some other things to consider about the life are that you're paid a negotiated fee plus tipping. The tipping is where the money is. Motivation to understand your job well! In the lodge I worked at we were basically with the customer from the wee hours of the morning until around 5:30PM, seven days a week for six months. I had maybe four or five days off the entire time. We were in a desolate area of Alaska with no phones and nothing other than float planes. boats, and the clients we guided for six months. There is a definate culture shock when you return to "the world". Driving a car the first time will freak you out! Hope my rambling helps