In my experience, a better way to approach your goals and build good habits is to set a schedule to operate by rather than a deadline to perform by.
Instead of giving yourself a deadline to accomplish a particular goal by (and then feeling like a failure if you don't achieve it), you should choose a goal that is important to you and then set a schedule to work towards it consistently.
That might not sound like a big shift, but it is.
The Idea in Practice
Most of the time, I try to be a practitioner of my ideas and not just someone who shares their opinion, so allow me to explain this strategy by using two real examples from my own life.
Example 1: Writing
I publish a new article every Monday and Thursday. Since my first article on November 12, 2012, I've been delivering two articles per week, every week. Sometimes the article is shorter than expected, sometimes it's not as compelling as I had hoped, and sometimes it's not as useful as it could be ... but it gets out to the world nonetheless.
Of course, I didn't always operate on a Monday-Thursday schedule. In fact, I came up with reasons for actively avoiding a schedule. I told myself, "I do my best writing when I'm inspired, so I'll just wait until I get the urge to write."
I assumed that if I wasn't doing my best work, then I shouldn't be doing it at all. The problem with that strategy is that my output was erratic at best.
It took me awhile to realize it, but it's not about always doing your best work, it's about doing the best you can on a consistent basis.
Once I stopped focusing on results and simply held myself to a consistent schedule, my work and my output improved. In the first 6 months after I started writing two times per week, I wrote more in quantity and better in quality than in the previous two years.
It doesn't matter what you're doing, if you only work when you feel motivated, then you'll never be consistent enough to make significant impact on your life.
Example 2: Exercise
In August 2012, I decided that I wanted to do 100 pushups in a row with strict form. When I tried it the first time, I only got 36.