Back in the day when I was learning the tone rules, I spent about 5-10 min nearly every day for 2 months going over the tone exercises found in the The Fundamentals of The Thai Language. I used it for years with my students and gradually over the past few months I’ve put together a better version that reflects words that you are actually going to be using. The purpose being that you are practicing working out the tone rules for words that you will eventually know and should be able to say correctly. Having the English would be distracting so there won’t be any of that. I’m off to Japan this weekend am I’m feeling particularly generous so here is the link to the drills I use with my students.
If you can go through the entire page and can work out each tone in under 5 minutes you are doing something right. If you aren’t there yet, remember to divide and conquer one class at a time.