As hard as it is to decide what to study, you need to discipline yourself to decide when to study. Set aside regular time, just as you would schedule an appointment or a work meeting. This is your appointment with Hashem...and with your future. Whether that time is weekly or daily, set it aside. Make it sacred. It's easy to allow that time to escape when a more immediate priority arises. Don't let that illusion distract you. That is your yetzer hara, saying, "You can always study some other time. This needs your attention right now!" (Check this post out for tips on how to deal with the yetzer hara!) But as with anything, there are legitimate emergencies that may require your time and sometimes you just need a break. When you miss your appointed study time (and you will sooner or later), don't beat yourself up about it. Resolve to do better today.
As Hillel says,
Do not say, "When I have [free] time, I will study," lest you never have [free] time.