how do i get my ex- girlfriend to love me again?

Date someone else and see how the ex reacts.  Her feelings about you
may change when she sees you with someone else.  And if they don't, to
hell with her.  You are worth someone who loves you back.  Move on, be
strong - most women are attracted to that.

http://www.pickupguide.com/layguide/

More information would be nice.

For example...
Did she break up with you, or you with her?  
Why did the break up happen?
Are you male of female (I'm assuming male)?

Depending on the conditions, different approaches should be taken.

Try answering these questions and it may help you to figure out what
exactly you want.

Did she love you at all before you broke up with her? 
Do you love her? 
Why do you want her to love you again?

There is a difference between having romantic feelings toward an
individual and loving an individual. Love is a learned behavior and
might take many years. Romantic feelings develops fast and are based
on physical attraction, common interests etc. You girlfriend can love
you, but may have romantic relationship with other guy. Are you ready
for that?

by investing VERY substantially MORE in efforts, love and money FOR
her than you do for finding the answer here.

if your offer for a solution is ( and most likely it really is )
proportional to the amount of efforts and love ytou gave her before
and are willing to give her NOW - then you may simply be too stingy in
love for her to be attractive TO her.
think about your values 
is she really only worth $2 to you
for 2$ you may not even get a magazine with pics ...
even less a real partner for LIFE .

it is the REAL offer of love that creates attrasction 
a sun that is dark and cold would never attract billions who love to take a sunbath

same applies to love
your love needs to be actually FELT by her
even when apart.

a girl can only miss the one who truly loved her so much that she was
FEELING happy ... feeling LOVED
day after day
ever improving