If you use Google Maps, entering sfo and fish camp, CA, it will give you 3 good routes to choose from.

Are you going to be doing any tourist sites in SF?
If you are going solely to Yosemite, You could fly to Oakland or Sacramento and save a little on car rental.
You could also take the San Joaquin train to Merced (or Fresno) and rent a car there to go into Yosemite.
You could leave Yosemite by way of the south exit going through Oakhurst. Be sure to see the Mariposa Grove in the southern part of the park.

Yes, I will be in SF for 4 days after Yosemite. I have been to SF before so wanted to see a little bit of Yosemite this time. I am planning on returning the rental car when I make it back to SF or might keep it for an extra day to visit Muir Woods.

I have seen a couple of routes but wasn't sure which ones might be more scenic. I always try to take a different route from the one I orginally take to see different things.

I hope you have existing reservations for the Park. Beginning in late April, Yosemite tends to be booked solid.

This is the website for reservations

http://www.yosemitepark.com/lodging.aspx

The site is a bit convoluted, but you can manage to find out if anything is free.

Thanks. I already have a place to stay. Fish Camp was all that we could get when my party made their reservations back in September that met our needs. The location isn't ideal but it was better than nothing, considering it might be the only time me make it to Yosemite.

I just wanted you to be aware that there are several closer airports to Yosemite besides SFO. Nearly anyplace you rent a car will be cheaper than the cars at SFO.

Thank you Tom. I do appreciate it. I had checked out the other airports and SFO was actually the cheapest for us when I booked some time ago. I probably should have waited as airfare had gone down some since I booked.

Highway 49 goes through scenic country and is loaded with history. When we drove it recently, we were delighted by the many charming old towns that dot the route: http://www.historichwy49.com/mainmap.html

HTTY

It seems that everybody is giving you some form of advice EXCEPT dealing with the topic you asked about. So let me give it a shot.

Fish Camp is between Wawona and Oakhurst. Thus you could either head right for Oakhurst and then to your lodging, visiting the Valley later, or go to Wawona after going to the Valley. I strongly suggest you do the former, simply for a magic effect that is impossible to experience in any other way than to enter the Valley from Wawona.

Specifically, seeing the Valley for the first time, in all its glory, all at the same time, when coming out of the Wawona Tunnel.
http://www.youtube.com/watch?v=iuOirOqnOcQ&hd=1
You'll feel the same way Dorothy did when she stepped out of her house into the Land of Oz.
The following is NOT a joke: be careful when you exit the Tunnel into the Valley, as the beauty will be so overwhelming that your brain will have difficulty adjusting. You will DEFINITELY need to pull over and adjust your thought patterns for a few minutes.

You may as well get to Oakhurst as quickly as possible, which means 580 east from Livermore, 205 and (120) towards (99) and Modesto, south on (99) towards Merced, then east from Merced on Highway 140. Get on Highway 49 at Mariposa, then head north on Highway 41 at Oakhurst towards Fish Camp.

When you are leaving Yosemite for the last time, spend the next hour or so (1) planning your next visit and (2) driving west on Highway 140 out of the Valley. When you get to Highway 49 at Mariposa, head north towards Coulterville and Jamestown. Stay on Highway 49 as much as you like, visiting Gold Rush towns along the way. Eventually you'll head west towards Stockton or Manteca, at which point just follow the signs back towards The City.

Thank you HTTY and Paul. This is the kind of information I am looking for. I would like to make the most out of driving to this area of the country. On my past trips, the way back hasn't always been the most exciting.

Check google maps. On the way to Fish Camp, it shows heading south on 101 from SFO to Hwy 152 east then on to Hwy 99 thru Madera. I would go this way to Fish Camp. On the way back to SFO, I like PaulRabe's suggestion of going thru Mariposa, Coulteville and the Gold Rush towns.

An interesting route through the valley on Sat is the Bay Bridge, through the Berkeley Hills, 4 and 160 through the Delta to 12 then 12 to San Andreas and 49 to Fish Camp. Anything else is boring freeway until you get to 49.
Coming back I would go 140 to Merced down to 152 on 59. Then left on 156 warning the thru trafic on 152 won't stop, 156 to Watsonville then up the coast to SF or stop in Monteerey for a while I would overnight there, but that would depend on your SF plans.