I agree with Lalita. It totally depends on your goal. If you aim just to communicate with people, starting with basic phrases would be enough, but if you desire to read Thai novel or work in Thailand, you might need to start from letters. Additionally, it depends on your learning style as well. Someone likes to watch drama, some like to chat, or some might like to read articles. These activities improve you different type of skills. It's up to you. :)

If u want to speak and listening u just learn vocabulary first (pronounciation later) coz our grammar not that hard. If u can remember lots of vocab, u pass 50% also no need to change verb,adj,plural,no gender. And u try to speak and listen to native. but if read and write it will take time

I prefer learning basic phrases. There are several websites and online dictionary that have basic Thai sentences (with audio), romanized script, and english meaning. You can listen to the audio then mimic the sound and record it. You can replay what you sad in Thailand, compare to the Thai audio on the websites, and practise. You will feel the progress of learning. Feel the ability to communicate on the basic subject. But if you are tone deaf, it will be difficult. Many of Thai students start learning english with learning a, b, c , vocabulary, grammar, then , ... Ten years after that they are still in the books and not able confidently speak english with the foreigners.

Take two hours to get to know all basic alphabets and vowels - do not have to full memorize anything.... just get to know them. Couple more hours to get used to the sound of words and how they are pronounced, try watching couple good Thai movies, avoid TV shows because these people do not speak proper Thai. get yourself a "Thai learning" book and learn phrases and words. it these steps work for you, you should be able to speak a little bit Thai with cute accents in no time. Having one or two Thai speaker friends can help to make thing easier. remember, learn it as you are a new Thai born.