Hard work. Dedication. All-consuming focus and drive.
Lingering doubt. Sleepless nights. Lots of prayer.
And sometimes will and determination is not enough and life overwelms you with distraction and everything comes apart.
Step back, regroup. Invest in more prayer because you can never pray enough. Learn something new. Take a nap. More importantly, take a vacation. Free, cheap, one day or one week... trust me, whatever it is, make the very most of it and come back recharged and ready to go again.
Because, if this is really what you want and you really believe that it's God's will for your life, then you will see it through. Period.