The easiest answer to this is “JUST START!” No matter how big or how small the task, make one step in the right direction. Do not get caught up in perfectionism or worry about finishing. Taking a stab at a dreaded task will show some self-discipline.
Self-discipline is an essential factor for productivity and success.  Without it, one becomes lazy, unmotivated, and dependent upon others.  Lack of self-discipline also makes for a difficult-to-deal-with employee, boss, or coworker.
Exercising self-discipline means, in an old-fashioned term, setting yourself to a task.  You need to know what must be done, when it must be done–  and do it.  Good self-discipline includes a basic schedule, or framework, of what needs to be accomplished within a specific period of time.  You do not allow yourself to become sidetracked, or to procrastinate.