Her are steps to building your enthusiasm:
Adopt a definite major purpose.
Write out a clear statement of that purpose and your plan for attaining it. Include a statement of what you intend to give in return for its realization.
Back your purpose with a burning desire. Fan that desire; coax it; let it become the dominating thought in your mind.
Set to work immediately in carrying out carrying out your plan.
Follow your plan accurately and persistently.
If you are overtaken by defeat, study your plan carefully, and change it if necessary. Do not change it simply because you have met defeat.
Ally yourself with others whose aid you need.
Keep away from joy-killers and naysayers. Stick with the optimists.
Never let a day pass without devoting some time furthering your plan. You are developing enthusiasm as a habit, and habits require reinforcement.
Keep yourself sold on the idea that you will obtain your definite major purpose, no matter how far away that moment seems. Autosuggestion is a powerful force in developing enthusiasm.
Keep your mind positive at all times. Enthusiasm will thrive in a field full of fear, envy, greed, jealousy, doubt, revenge, hatred, intolerance, and procrastination. It needs positive thought and action.
Does this list sound like things you are already doing? It should. Enthusiasm it the natural outgrowth of all your efforts toward success. What is important is that you now recognize that every appropriate move you make is building your enthusiasm as well. Understand how it has helped you, and you will be in a better position to apply this tool consciously when you need it.