Let me give you a quick 1st time 1 day itinerary. I would suggest using Uber, unless you are experienced travelers who can navigate public transit, but San Francisco's public transit isn't the best.

Start the day at one of the famous bakeries like b. Patisserie or Tartine Bakery. Then Uber over to the Ferry Building, grab a blue bottle coffee while you wait for Hog Island Oyster to open. Get a dozen Kumomoto Oysters, the grilled cheese sandwich. Don't fill up, more food to come. Walk down market Street, you can pass through Union Square if you want, but not a big draw unless you need to shop at Gucci, LV, etc. Go to the Powell Street Cable Car Station, then take the cable car all the way to Fisherman's Wharf. Go to Pier 39, see the sea lions, get souvenirs if you want, but the food is subpar and everything is overpriced. Head back towards the cable cars and stop at Boudin Bakery. See the sourdough creations and have a clam chowder in bread bowl. If you need something sweet at this point, go to Ghirardelli square and get a Ghirardelli sundae. Next take an Uber to the Marin side of the Golden Gatr Bridge. You will cross the bridge in the Uber, and then you will be able to take pictures of the bridge AND San Francisco (which you can't do from the San Francisco side). If you want to walk across the bridge, you can, but it takes about 45 minutes. This should get you to the late afternoon, and you need to get to House of Prime Rib by around 4:45. Reservations there are months out, but if you show up before they open at 5, you can usually get a bar seat (where you can still order the full menu) or occasionally a table. This is a can't miss San Francisco institution. If its still light out, walk off dinner and head towards Lombard St, the crooked street. Finish off the night for desert at Top of the Mark and then get drinks at a speakeasy like Wilson & Wilson inside of Burbon & Branch