Read his book. "Sanford Meisner on Acting" is the late Sanford Meisner's manifesto on his belief and system of acting. Before you can begin to learn the technique, you must understand it. This book is carried in a variety of theatrical bookstores or is available for purchase on-line.
Surf the web. So you've read the book, and now you are ready to train as an actor in the Meisner technique. The best way to find a teacher is to go on-line and search for people in your area who practice his discipline. This will be easier in the major cities. However, if you can't seem to find anyone in your area, consider forming a group with your friends.
Contact the teacher. Discuss your goals and ask if you can audit one of their classes. This is a common practice among acting classes and should be no problem.
Take the class. If you enjoyed your experience auditing, sign up for the acting class and begin to take lessons. Before you know it, you'll be in the movies!
Practice! The fabric of the Meisner technique is steeped in an exercise called "repetition" where two people "repeat" things to each other that they notice in the other person. Only when you notice something new, do you change what you are saying. For instance one person might say "you have a blue shirt," the other would repeat "you have a blue shirt," until the first person notices "you have black hair" and the other would repeat "you have black hair." Eventually this continues until you are noticing emotions, "you're mad at me" and finally you try and sway someone to share your point of view by using different tools. (yelling, laughing, cajoling) or whatever it takes to "get what you want." The greater point of the exercise and the technique as a whole is to get you working off the other person so that you are connected and their emotions feed your emotions and vice versa.
Have fun! Acting is supposed to be fun, so while you should take your craft seriously, make sure you're continuing to have fun as you explore the technique!