Think of profound things to say. Yoda was a master of philosophy and everybody looked to him for wisdom. He was the pinnacle of intellect and, as such, you will need to have some phrases that will inspire and educate others.
Learn Yoda's sentence structure. In most of his phrases, he begins with the verb that we would normally put in the middle of the sentence. He then ends the sentence with the words that we would typically begin the sentence with. So, for example, the phrase "You will be a great Jedi" becomes "Be a great Jedi, you will."
Add the negative in a sentence to the end. Using the example in Step 2, the phrase "You will not be a great Jedi" easily becomes "Great Jedi, you will become not." Likewise, Yoda would often add a "yes" to the end of an affirmative statement - "You will become a great Jedi, yes."
Attach the following at the end of a question - "hmmm?" Yoda often added this after asking somebody a question. Use an upward inflection as you say it, too.
Practice trying to talk like Yoda. When watching television, turn some of the phrases into "Yoda phrases" in your head. As you read the newspaper or magazines, think of how Yoda would say some of the sentences as you read. The more you do this, the quicker you'll be able to imitate the little green creature's way of speaking.
Amuse your friends with your new talent. Even people who are not fans of "Star Wars" will understand what you are doing.