If you are in school, write for a living or want to blog for money, you have to be able to write consistently. Some writing professions, like journalism, involve regular deadlines that can aid the reluctant writer by creating a fear of failure that surpasses the impulse to avoid.
Many writers who seek to make money eventually with their writing (bloggers, novelists) don’t have the kind of immediate deadlines that are most effective for nudging authors past their resistances. Countless impoverished literary hopefuls flounder in wordlessness as a result.
If you are floundering, you may want to start using short-term deadlines, and build in some sort of accountability that will improve the odds that you will keep to them. Tell a good friend what you are planning to do, take a class where you have to report on your progress, join a group where you discuss your project and set goals regularly.
If you have historically been unable to set internal deadlines and meet them successfully, accept your limitations without shame and build in some external structures that assist you with staying on the horse.