Twin peaks offers a good view of the entire city, though you can't get a great view to Golden Gate Bridge. It's better to go to lands end for that. The trek to twin peaks isn't challenging. It depends on where you start. The best way is to take the 48 route and get off at Portola. You can also take route 37 and get off at the eastern side of twin peaks.
I took 48 and walked up the twin peaks road. There's a path next to the road to make it safe. After walking for 5-10 minutes you will notice brown stairs leading up. Take them and continue taking brown steps whenever you see them. The entire trek took about 20 minutes and wasn't difficult.
Carry water and snacks if you want a snack. A wind breaker is a must since it's pretty windy up there. Plan to reach there close to or after noon otherwise it'll be too foggy to see anything. More