You might get more help if you were more specific as to which rivers and what salmon species you want to catch. If I had to start from square one I would get three books. Drift Fishing for Steelhead, Spoon Fishing for Steelhead, both by Bill Herzog and Spinner Fishing For Steelhead Salmon and Trout by Jed Davis. Even though they are written for steelhead the information,in general, can be applied to salmon with some variations. Most of the books that I have read on river salmon fishing are 90% fishing stories that don't have much useful information past the very basics of the different rigs. Another source of good info are the tips section of river salmon guide web sites like this one or sites of gear manufacturers. The search funtion of this site is a gold mine of information. There is massive information available using google search. All that will get you part way there. The rest is getting to know your river up close and personal.