ALWAYS END ON A GOOD NOTE

Example: If you’re talking on the phone and the conversation is fun and easy, although it may not be your initial instinct or desire to do so, end the call. 
If you’re out on a date, just at the point things are going well politely say you have to go. In other words, when things are going great, cut out.
Just like a good book or a movie that you wished would never end, she might wish the date or call was longer, but she’ll ultimately end up wanting you that much more. It’s a win, win situation. You can only come out ahead.