If you're not from there, paying a guide is not only a good idea, but required in some instances.
If you're just going salmon fishing, no guide required...follow the crowds to the big fishing holes and do what the other folks are doing (learn quickly, since combat fishing doesn't tolerate new guys very well).
Halibut fishing - charter boat needed.
Hunting - guide mandatory in most/all cases for non-residents, unless hunting with a close relative who is a resident.
Keep in mind that in Alaska, a 20-minute hike can turn in to a survival situation if you are not prepared...happens every year -- tourists go for a quick hike and end up on the wrong side of a mountain... get flown in to a lake to fish and return flight gets weathered out for longer than their provisions, etc... Wonderful place, but not very forgiving....