Self discipline gets stronger as you use it more often. As a child your self discipline grew as you did, and as an adult some of the things you struggled most with as a child probably are no longer issues for you. The goal to greater self discipline is to use it. Force yourself to make changes every day that will focus your attention on increasing your inner discipline.

Stop procrastinating: It's true, we all put things off from time to time, but habitually pushing things back until the "right time" is a sign of weak self discipline. Set a plan in motion to kick that non motivation. Write down simple goals for your day and stick to the plan. Interruptions happen, so plan for distractions in advance and keep your mind focused on the tasks at hand and the goal for the day. This small step will start training you to look at the broader picture in life and set goals bigger than daily tasks.
Kick one bad habit, then another: Pick something small, but that could actually make a difference in your life. Maybe you add sugar to your coffee each morning. Those added calories don't make much difference in taste, but could certainly change your overall health. Start by getting rid of the sugar. Not only will you have to become accustomed to a new taste in your coffee, but you'll be willing yourself to stick to it until that taste actually becomes pleasant and you like it better that way. Once you've accomplished a small task like this, you can move on to something even bigger and know that you can accomplish it, one hour at a time, one day at a time.

Train your brain: There are some simple exercises associated with increasing your concentration and memory. All of these exercises require mental stamina and the discipline to work on them each and every day until they become second nature to your character.

Pick a simple thought and see how long your can keep your mind on this particular thought. Make it a daily habit to concentrate on this same thought every day for 5-10 minutes. If other thoughts drift in, push them away as best you can until you can easily keep other ideas from invading your head.

Find a comfortable, straight chair and see how long you can sit completely still in it. Focus your attention on sitting still since you'll still have muscle movements the first few times. Start off with 5 minutes and as you get better control of your body, increase your time to 10 or 15 minutes.

Take notes to help you stay organized with your thoughts. Experts agree that short term memory can only handle seven thoughts at a time so prioritize and write notes on anything past that amount to help you focus on tasks beyond that.

After you've learned something, relay that information to someone else. Teaching others and having to explain your new information in your own words is a great tool for increasing memory.

Re-learn a subject from school that you may have forgotten or don't use often. As boring as this is, it's important because it forces you to be committed and disciplined while you learn it. It encourages you to use your whole brain. Once you've learned this information, share it with someone else. Having to explain what you know is a great tool for increasing memory.

Set an achievable but difficult goal: Push yourself to achieve something you haven't been able to in the past. Whether it's weight loss or to quit smoking, it's going to be a difficult test of your internal discipline. Make your progress measureable and reward yourself when you meet certain points along the path so you'll stay motivated to continue on.