Purchase a notebook or journal. Rather than grabbing any old piece of paper, acquiring a brand new journal is really your first step in learning how to push yourself mentally. Your goals and aspirations are important and by making the effort to buy a notebook in which to record them, you are giving them the distinction they deserve.
Write down your goals in the notebook. If you have several, section off your notebook accordingly. The act of recording your desires has the effect of making you feel accountable. Accountability is a key component in learning how to push yourself mentally. When what you want to accomplish is in print, it's harder to ignore. Put your notebook somewhere in sight all the time.
Challenge yourself to achieve just one step toward your goal. Pushing yourself mentally doesn't have to be an onerous task. Make it a game with a reward system. If your goal is to work overtime to earn enough money to make a big purchase, task yourself with working overtime from Monday to Thursday, and work your normal hours on Friday.
Track your progress in your notebook. Buy gold star stickers or write the word "win" beside each success. Mental discipline and delight in your achievements are not mutually exclusive. In fact, the more you push yourself mentally to produce results, the more results you'll see, which will in turn feed your determination and sense of accomplishment.
Work at giving yourself credit. Learning how to push yourself mentally is a noble goal. It means you recognize that discipline is a necessary skill if you want to actualize your dreams. Any negative self talk you may have once indulged in has to be replaced by positively affirming your determination to break old habits that don't serve you anymore.