It's common for friends and associates to complain with frustration that good Thai girls don't take interest in them. Here is my collection of things to consider and suggestions:
Thai ladies are usually shy and will have to know you over time before they will become what you may consider a girlfriend.
Thais are very sensitive to things that may affect their reputation and status, and are cautious.
Most good Thai girls are virgins or have had very few and discrete sexual experiences with very few boyfriends they knew over time.
Outside the farang areas, you are moreso an alien farang and may be considered a typical prostitute-oriented farang until you prove otherwise.
Dress nicely. Thais are more sensitive to dress, cleanliness and appearance than foreigners.
Learn about the Thai values of maintaining your cool and controlling your temper at all times, being polite and respectful (which is how you project yourself as respectable), and being easygoing and nonthreatening.
Thais are very sensitive to body language. As applies to Hollywood, "Bad actors act, good actors are", i.e., don't just act a certain way, be that way.
Don't be too much on the hunt. Whether at the workplace or in an entertainment area, don't look at too many girls with interest. Most girls don't want a playboy.
Smile. This is the Land of Smiles. Again, "bad actors act, good actors are". Think pleasant thoughts where you're genuinely smiling to yourself before you walk into a social environment. This is Thailand, and if you want the Thais to like you, then you need to be easygoing and have a good kind of smile on your face.
Of course, many of the things I recommend for Thailand are true most everywhere in the world, each to varying degrees. Thais are a sensitive and gentle people, and some of these elements of human nature carry more momentum in Thailand.
Some things that work well in other cultures are counterproductive in Thailand among good girls:
Being too assertive
Machismo
Straight talk when there are gentler alternative ways to say the same thing
In a work environment, you will get to be known over time, and this will affect not only what secretaries (and their friends that they bring to social events) will become available to you, but also which subordinate employees will stick to their jobs, how well they will work for you, and indeed may affect whether you keep your job.
Never make a Thai lose face. If you have a criticism, keep it private, do not display it in public. When you do criticize, raise the issues gently and gradually. There are many ways to communicate the same thing, and if you choose the more sophisticated and diplomatic way, the results will be much better. (Venting steam for your own satisfaction is dumb.) If you make Thais fear you, then you can't expect any of them to like you in an amorous way. If you introduce an explosive and unpredictable nature over time, what result do you think that will produce? On the other hand, if you show self-control when under pressure and during the bad times, that will be reassuring.
The power of money does not produce the same results in the office as it does in the massage joints and in many western environments with "matrimonial prostitution".