This is my first time heading to the states in August. Will be coming back next year in January.
It's my first time getting tickets for such long flights.
Longest flight for me is probably to Japan.
Any tips on how I can get promotions for flights to San Francisco?
Any advice on which airline to go for and what sites to purchase the tickets?
I am looking for economy class and comfort given the long flight time.
1) Be open for flights through other gateways. You can get to San Francisco hundreds of different ways from Singapore - through Hong Kong, Manila, Shanghai, Beijing... Don't forget about other possible ways to get into the country, as well. Instead of flying direct to SFO, it might make sense to go in through LAX (Los Angeles) or HNL (Honolulu).
My usual when I lived in Singapore was Singapore Airlines through Seoul (ICN) to SFO. It's not the rock-bottom cheapest, though - the cheapest will probably be on Chinese or Taiwanese airlines. They won't be as nice, but it'll get you from point A to point B.
Check out Hipmunk - it's pretty good at finding the cheapest flights with the least amount of pain.
2) For promotions... you can sign up to airlines' mailing lists and see if any discounts turn up, but honestly you're better off just using Hipmunk. It finds most of those discounted fares, and you don't have to get spammed.
3) Which airline... yeah, don't fly the American airlines (United, American, Delta). Their service absolutely blows, but it's still better than it was. Some American airlines (Virgin America, Hawaiian, Alaska, JetBlue) are pretty good, but they don't go trans-Pacific (well, Hawaiian does, and I love them to bits, but they don't go to Singapore).
I'd pick Singapore Airlines or Cathay if your budget stretches that far. If you need rock-bottom cheap, like I said above, look at the Chinese or Taiwanese carriers.
4) Also, as someone else said: fly midweek! Tuesday or Thursday flights will probably be a lot cheaper for you, because they're less popular days to fly.
I had a quick look on Hipmunk and found a couple of options, using Tuesday August 16th to Thursday January 19th as some sample dates: Air China through Beijing was $1100 or $1200 USD for the round trip (but with some LONG layovers in Beijing), and Philippine Airways through Manila was $1200 USD round trip with a reasonable 3-hour layover in Manila.
If you travel out a day later, on Wednesday August 17th, you can do it for just $1000 USD r/t: Air China through Beijing, leaving at 12:15am on Wednesday with a 9-hour layover in Beijing. The scheduling's absolutely miserable, but that's a pretty great price.
Enjoy the trip! You'll love it over here.