This what I've found keeps me on fire and committed to serving the Lord...
Be around people who are on fire for God!
One day you might feel down in the spirit. When you around at least one other believer, they will be there to lift you up and encourage you.
For if they fall, one will lift up his companion.
But woe to him who is alone when he falls,
For he has no one to help him up. (Ecclesiastes 4:10)
Do not be unequally yoked together with unbelievers. For what fellowship has righteousness with lawlessness? And what communion has light with darkness? (2 Corinthians 6:14)
Do not be deceived: Evil company corrupts good habits. (1 Corinthians 15:33)
He who walks with wise men will be wise,
But the companion of fools will be destroyed.
So a man sharpens the countenance of his friend. (Proverbs 27:17)
not forsaking the assembling of ourselves together, as is the manner of some, but exhorting one another, and so much the more as you see the Day approaching. (Hebrews 10:25)
As you can see, there is power when believers gather, sharpen each other, and are there to pick each other up. In Mark Chapter 2 the paralytic was healed because of his friends' faith who went through the roof to bring the paralytic to be healed by Jesus. Surround yourself with people who will do the same for you.