Learn them like they were a big word. For example, "Nice to meet you" has four syllables--so does "interesting." Just like you can learn the word "interesting" and when to use it correctly, you can do the same with the phrase, "Nice to meet you" and all the others. Also, learn one phrase perfectly before trying to learn different versions of it (e.g., "It's a pleasure to meet you," "delighted to meet you," "nice meeting you," etc.).