Tones are the core of the Thai Language.
For a person learning Thai, the five tones are the starting point. For those who are already fluent, tones are both a source of joy and frustration.

I've been speaking Thai for about 30 years. I learned most of my Thai by drilling words and phrases, over and over again. The key is to focus on getting exactly the right tone for each syllable. I set a rule for myself -- "If I'm not sure of the tone of a particular word, I don't want to know that word until I'm sure of the tone." The reason for this rule is that un-learning is more problematic than learning! I simply do not want the wrong tone nesting itself into my little brain. I find it much more effective to allow entry only to accurate pronunciation.

If you focus on good tone quality, right from the beginning, it could save you many years of floundering in Psuedo-Thai. What is Psuedo-Thai? It's thinking that you speak the language because you can pronounce vowels and consonants. You can put "words" together, but your tones are "El Garbage." There are lots and lots of foreignors who fall into this category. They might be understood by their Thai girlfriend, but hardly anyone else.

Schools that teach Thai, for the most part, have abandoned the teaching of tones. This is probably because many new students, perhaps most, have great difficulty breaking the tone barrrier. Schools come to realize that an emphasis on tones will hurt their bottom line. Students will become frustrated and disgrunteled. They may seek more comfortable alternatives.

Don't be fooled. Don't let anyone tell you that tones are unimportant. Thai is a tonal language; this cannot be avoided. Get used to it. If you want to learn to speak Thai, tones must become the top priority. Practice your tones. Drill. Say it again. Say it again. Eventually, you will break the tone barrier. I know, because this is what I did 30 years ago.

Now, I am the author of Thai Language Course, 5th Edition, Published by TigerPressThai.com