The ropes on the SF are pretty simple. Try and elk hair caddis in the evening, or an elk hair caddis in the morning\day with a dropper (about 12 inches of light tippet tied to the bend in the hook of your dry) like a copper john, prince nymph, or hairs ear.
Pick an exit from downtown NB all the way to the pass. park by a bridge or other access spot and start hiking up or down stream (i like to go the direction that I think will take me to less pressured water). Hit the nice looking spots with a few casts here and there but move fast until you are 1/2 mile from the access point. Then start working a little harder. If you don't find fish (some stretches are just plain barren of fish), scratch that area off your list and try another one next time. Cast to the nice deep pools, but don't overlook small riffles and especially pocket water (faster water in a boulder field). The fish will hang in front, behind, in the seams, and pretty much anywhere they can hold and abush food as it comes by. the dry with short dropper works great in pocket water like this. It is hard to keep the fly in the zone long (a few seconds is all it takes sometimes), and with the dry, you can see exactly where the dropper is and know when it is in and out of the zone. I like to think of it as 'picking pockets'. It can be a blast once you get the knack and find a stretch with decent numbers of fish.