The cure for your lack of willpower depends on what causes it:
Many previous failures. If you too often fail, eventually you understandably figure it's not worth trying. In other words, you lose willpower.
The usually most successful solution: Choose more attainable goals: an job better suited to your strengths, a more attainable romantic partner, etc.
Hedonism. Here, you fail to realize that to the extent you prioritize pleasure over productivity, you are a drain on your family and on society. The wise person realizes that productivity is key to the life well-led, and that requires frequent impulse control and sacrificing of pleasure for the greater good of accomplishing something.
Genetically low energy. Some people emerge from the womb driven while others are laid back. That is very difficult to compensate for. It may help to pair up for work and avocationally with someone with moderately higher energy. It may rub off.
If you have long been depressed (not just because of a specific situation you're facing,) drugs such as Prozac or Wellbutrin may help, especially if combined with regular exercise and short-term cognitive therapy.
Drug or alcohol problems. The stereotype of the lazy pot smoker is true. To find willpower you must find the--well--willpower to stop doing drugs and alcohol. You are fooling yourself if you think it isn't hurting your work and personal life, not to mention your health.
People of faith are often best helped with a 12-step program such as Alcoholics Anonymous. More purely rational people are often helped with cognitive therapy. Some people are helped by a physician-prescribed drug that reduces cravings or makes you feel nauseous if you drink or do drugs. For some people, a combination works best. Here is a review of alcoholism treatments.
You're pampered or have been. For example, you were too often indulged by your parents, you're a trust fund baby, welfare recipient, or have a spouse or parent who pays your bills. Unless you're an intrinsically motivated person, if you're taken care of, you lose much willpower. The following may be unrealistic but it may be wise: Cut the purse strings and try to make it on your own. Much easier said than done, I'm sure.
Unearned high self-esteem. Many people have been led to believe they deserve high self-esteem merely because all people are worthy or because they're "The Chosen People," "Black is beautiful," etc. That mindset is likely to reduce your willpower. True self-esteem comes only from accomplishment. If you think otherwise, you're deluding yourself.
Misinterpreted theology. Some religious and otherwise spiritually oriented people believe canards like, "The world is abundant. It will provide" or "If it's meant to happen, it will," Many people misinterpret the Christian precept "Do not be willful" as "God will provide," rather than "Make all reasonable effort but at some point realize it's out of your control."
Along with intelligence and ethics, nothing is more key to the life well-led than willpower. I hope you might find at least one of the above suggestions helpful in improving yours.
Reactions to this article, including other suggestions on how to build willpower are, of course, welcome.