The separation has taken place, not without reason.
You may or may not have been told the cause of the breakup, yet you might take a guess, so you are cautious in the future.
But you now want your ex to feel desperate to have you back.
Take the break up casually.
Do not cry and fret over the breakup, especially in the presence of your ex or someone who will carry tales to your ex.
Pretend as though nothing unusual has happened and that your life has not come to a standstill.
Carry on with your regular activities and as a matter of fact include some new hobbies or activities in your schedule.
Give your ex the feeling that you're better off without them.
When your ex hears of you being better off without them, they will think of taking a about turn, towards getting you back.
But wait! Do not give in just yet.
Go about your life as though your ex had never existed in it earlier.
You want to make them desperate to get you back.
Just let go and enjoy life.
When your ex sees how care-free and happy you are without them they will feel dejected and desperate to want you back.
They cannot see how you could be enjoying life and having fun without them.
Your ex should be allowed to come to know of your enjoyments and care-free lifestyle.
Make your ex call you in desperation to get you back.
See that some time has passed before your ex has decided to call you to get you back.
If it's too soon after the breakup ignore the calls but if a comfortable span of time has passed then respond to the calls.
But do not show your eagerness just yet to fall prey.
Let them be at the begging end for sometime before you decide to give in eventually.