September and October work best—fog clears more often, temps hit 18°C–24°C (65°F–75°F), locals call it their actual summer. June through August is tourist season, but the fog stays thick most mornings, burning off by afternoon, sometimes. March to May has decent weather and fewer crowds. From November to February, it rains, and temperatures drop to 10°C–15°C (50°F–60°F), but hotels are less expensive. Pride Week in June significantly raises prices for hotels.
SFO Airport sits south of the city—BART trains run straight downtown, which is cheaper than rideshares that often hit surge pricing. Oakland Airport, across the bay, sometimes has better flight deals. Direct routes from most US cities, as well as international flights from Asia, Europe, and South America. Airlines compete on West Coast routes, so compare. Book six to eight weeks ahead for reasonable prices. Midweek flights often beat weekend rates if you have flexibility.
US citizens don't need anything. Visa Waiver countries get 90 days with ESTA. Others need standard US tourist visas based on their passports.
Stop saving Golden Gate photos—book your flight to San Francisco and get to a city where tech money crashes into old neighborhoods, the food's legitimately good, and hills make walking feel like exercise you didn't plan on.