B.F. Skinner, the father of behaviorism, would point you to "shaping" of behavior. Successive approximations of the behavior reinforced over time. So, if you want the dog to give you it's paw you can start with getting the dog to look you in the eyes and giving a treat. Then, once they've looked you in the eyes you give them a treat for sitting down. After that you give a treat after holding their paw.

http://wik.ed.uiuc.edu/index.php/Shaping_behavior

You get the idea.

Now, you're dealing with yourself so I think giving yourself modest goals and rewarding yourself for them is a great way to accomplish this. If you really want to be a runner start by getting yourself to go for a walk after dinner--of any length. Heck, walk around the block once. Then try walking around two blocks. Write it down in a book and celebrate these little victories: "I walked five days in a row for a total of 40 blocks... oh wait, that's two miles!"

What you'll find is *starting* is the hardest part. So, make the challenge to yourself the start.

If you don't eat veggies start by challenging yourself to just eat one apple a day. Don't look at it as food, look at it like a game and you won the game by doing it.

It's also very motivating to look beyond yourself and get a partner. Going for a walk with someone or shopping at the farmers market together (which includes walking), should make the activity more interesting.

I play poker on a regular basis because of the friends I have who play, but when I was in New York City my friends played basketball. I need to get a group that is active together. So, self-motivate yourself to join a group! :-)

Self-reporting is a key part of the process. So write a journal about your runs, walks, whatever.

Also, I'm not a psychologist... if you've got serious problems you should talk to a doctor about it.

1. Get rid of word "self-discipline" from your vocabulary. Successful people have different habits than unsuccessful people, happy people from unhappy people. A habit is a discrete observable behavior that if you maintain for 21 days becomes a habit that takes little energy to maintain after that.
2. After you select the behavioral change you want to make, contact a person who you respect and cares about you. Tell them that you are committing yourself to overcoming a self-defeating behavior, tell them what you're going to do different and then ask them if they could contact you by email or phone in two and then four weeks to see if you have followed through. You'll find it difficult to break a commitment to someone that you respect and that you don't want to be disappointed in you.
Mark Goulston
author - Get Out of Your Own Way: Overcoming Self-Defeating Behavior

It is imperative that attention is paid to self-discipline. Without it, no self improvement plan can be
successful. Inculcating discipline in your daily life and routine need not be a difficult exercise. A few basic tips are:

*Start small
*Just do one thing at a time
*Don't allow others to lure you away or distract you
*Handle weak moments with strength and will power
*Try and adjust different circumstances into your lifestyle
*Don't talk too much about your decisions
*Mark each milestone as it is a great motivator
*Make charts to mark your success
*Don't get discouraged by a fall or slip. It’s part of life. Take it in your stride.
*Reward yourself for each success

Start with something you like to do and decide to do it everyday. It doesn't have to be anything beneficial or important just something you like to do. For instance, say you like playing Literati. Play it everyday at a time you set for yourself and if you don't feel like playing at least log on and go to the page. See how long you can keep it going. And when you fail to play Literati for a few days don't be too hard on yourself, just dust yourself off and start again.
When you can do something you like consistently you may develop the tools you need to do something you feel you "should" be doing.

Altering a person's general tendencies is largely about "carrots and sticks".....

If a person designs rewards for themselves, it can help. Disincentives are a bit harder, though having a partner can help with designing such a plan.