If you're not Asian and you don't know anyone in country, then you're climbing an uphill battle, but it also makes these tips even more important.
1. Don't Dress Like a Backpacker
Once you walk off the airplane at BKK airport and go to immigration, there are going to be lines to the right and to the left. The left is for visitors, the right is for citizens. As you can guess, if you take a look, then citizens do not dress like they're on a backpacking expedition.
Bangkok is a large metropolis. In downtown Bangkok, you're going to find High-End Luxury shops, such as Hermes, Prada, YSL, Salvatore Ferragamo, Chanel, Burberry, and more. The same stores that one would only find in the largest cities in the USA, such as New York or Los Angeles. While obviously most of those stores are there to serve Chinese Tourists, it should still give you an understanding that Bangkok Thais are very fashionable, trendy, and stylish.
When trying to think of how to dress to fit in, think Manhattan in the Summertime.
2. Don't Travel With a Backpacker Type Backpack
You can probably see a theme here, I'm trying to get you out of the Backpacker mindset right off the bat because once you do that, you'll blend in much faster and have a more local experience.
Travel with a normal rolling suitcase. While traveling with a suitcase will automatically put you in the tourist category, don't make it worse by looking like the cliche western backpacker. Upper-Middle Class Thais travel quite a bit and when they do, they take normal suitcases. Who wants to carry up to fifty pounds on their back when they can roll it, especially in a city with taxi cabs, elevators, escalators, and paved sidewalks and roads.
3. Don't Stay at a Hostel
Last tip in regards to getting out of the backpacker mind frame. On Agoda, I can book a Four star hotel one week from now, with traveller reviews starting at 8.5 stars at $45/night. There are literally one star hostels that cost more. If you're going to a hostel to meet other travelers so that you can travel with other backpackers, then so be it, but that's not really the point of this blog post.
4. Don't Order Pad Thai, Order Pad See Ew
It wasn't until I went to visit my wife, Anne, for the first time in Bangkok did I realize that most Thai people really don't eat Pad Thai. For the most part, Thais opt for Jasmine White Rice as their carb, just as with most other Asian countries. If they're not eating white rice, then they're having crab fried rice, Mama Instant Noodle in tom yum soup, Japanese ramen, sushi, Chinese ho-fun, Chinese chow mien, Italian Pasta, etc. I don't know, Pad Thai just seems to really rank low in terms of preference from my observation of my wife, family, and friends. I think the only thing that might rank lower than Pad Thai is Vietnamese Pho. Unlike parts of the USA, Vietnamese Pho just isn't on the radar of Thais.
So, if you want a Thai noodle dish, then opt for Pad See Ew. Thais are much more likely to order Pad See Ew than Pad Thai.
5. Do Eat Non-Thai Food
Following the previous logic, Bangkok Thais eat a lot of non-thai food, just like most people in big cities in the USA or Europe. They probably still prefer Asian food in general, such as Japanese and Chinese food, but you're going to find a lot of international cuisine throughout the city and thais do put their own spin on it. For example, Tom Yum Pizza and Pasta are pretty common dishes at Italian eateries.
6. Don't Hang Out at GoGo Bars
Hopefully this should be pretty obvious, but the only people at GoGo Bars are foreigners. From what I've heard, that includes the women because many are from across the border like Laos, Myanmar, and Cambodia. I'm not going to stay too long on this tip since if you're interested in going to a GoGo Bar, then you're probably not too worried about looking like a tourist
7. Don't Get a Massage, But Do It Anyway
The most tourist thing you can do is get a Thai Massage at some place like Health Land. These places are filled with mostly Chinese and Western tourists. Most Thais actually rarely get massages and if they do, then they opt for a nice foot massage.
But at the same time, who can resist a Thai Massage! Honestly, I can't afford one in the USA so during a one week trip, I try to get at least two in before I leave. So, if you don't want to look like a tourist, then don't get a massage, but sometime it's worth it because let's face it, you still are a tourist. Just make sure to hop on TripAdvisor to find a reputable one, which generally means clean, comfortable, calm facilities.
8. Don't Take a TukTuk
As previously mentioned, you're generally going to be able to find a taxi cab, take a skytrain, metro, or bus if you're around Bangkok. Just like any major city, those are the major forms of public transportation, not the TukTuk. Bangkok is too hot and, unfortunately, too polluted to actually enjoy taking a TukTuk so I personally wouldn't even recommend it as a tourist experience. If you want to look like a real local, then hop on the back of a scooter/moped.
9. Skip Pattaya, Head To Hua Hin
Hua Hin is literally almost the opposite side of the Gulf of Thailand in relation to Pattaya. While plenty of Bangkok Thais do go to Pattaya, plenty also go to Hua Hin and a lot less foreigners know about it, though that trend is changing.
Pattaya is like a shitty Spring Breaker city, while Hua Hin is basically for people who hate shitty Spring Breaker cities. It's still a tourist seaside city, but it's much more popular with actual Bangkok residences and probably because there are a lot less annoying foreign tourists.
10. Do Take a Lot of Pictures Like an Asian Tourist
There is a reason why Canon and Nikon, the two most popular camera brands for professional photographers, are Asian corporations. If you're ever travelled to Japan during the Cherry Blossom season, then you'll see that the majority of people taking photographs are actually Japanese and not tourists.
I do believe the stereotype of the Asian tourist with the camera is true, but with the advent of the selfie, SnapChat, Kardashian, Outfit of the Day, Americans are making up for lost time.
If you want to feel like a local, then don't be afraid to whip out the camera for a selfie or basically taking photos of whatever you like. Taking and sharing great photos is a very Thai thing to do, so don't be afraid to do so!