In order to "move on" you have to be willing to "let go".
The first step is to accept the fact that it's over!
As long as someone holds out hope for reconciliation they're not going to be able to (move on). Some people elect to "romanticize" the past using "selective memory" to recall only the good times they had.
Sometimes people will continue to surround themselves with reminders of their exes. They have some of their personal belongings in their home, framed photos out on display, remain connected through social media, sharing friends, going to places they use to frequent as a couple, wearing or using items that were given to them by their ex...etc
Is it any wonder why they're having a difficult time moving on?
Probably the best thing to do is box up all reminders and put them in the back of a closet/storage for safekeeping. Cut off all contact from the ex, block phone numbers & emails, unfriend them in all social media context and make your profile only viewable to real friends.
Don't buy into the theory of going from being "red hot lovers" to "instant platonic friends" who are like brother and sister.
The best friendships between exes usually occurs after a large gap in time where both people have moved on to other relationships and have fallen in love. Maybe they bumped into one another and decided to exchange emails to catch up.
Instant friendship however is usually a consolation prize being offered by the person ending the relationship so they won't feel like the "bad guy". Unfortunately the person being dumped sees it as an opportunity to possibly reunite as long as they can still be in their life.
Grieve among your best friends & family, rediscover old hobbies & interests you may have neglected, focus on getting into shape, your career, make new friends who have similar interest through Meetup.com which has group meetings, consider researching top online dating sites but first figure out what traits you want or desire in a mate.
Remind yourself of the facts of reality.
In order for your ex to have been "the one" they would have had to see (you) as being "the one". At the very least a "soul-mate" is someone who actually wants to be with you! (And vice versa).
There are over 7 Billion people on this planet! Odds are in everyone's favor there are more than a few people who would make ideal mates for us.
That man/woman you believe you can't live without just know there are billions of us who are doing so everyday!