I probably struggle with this even more than you do, so I don't really have advice to give, but I did want to share what I am trying to do to improve my discipline. It's difficult -- I have a big imagination, big enough even to visualize myself being very disciplined and productive. (I suspect you have a similar problem.) And yet, because of this, I am easily distracted, and when my grand schemes fall apart -- perhaps because I slept until 8:00 instead of getting up at 6:00 -- I am far too likely to abandon the endeavor for the day.
I am trying to avoid the mindset of waiting for the next fresh start. Discipline has to be worked out moment by moment, not just day by day or week by week. There is no excuse for giving up on the rest of some arbitrary unit of time and waiting until some later point (tomorrow, next week, next year) to really get serious. I slept late -- so I will still pray quickly before class, and then pray longer later in the day. I have to apply my imagination to seeing the intermediate steps between where I am and the grand vision. I need to take smaller bites! So these are my practical goals for myself, for whatever they may be worth to you:
1. Pray more. I am very bad at this, but when I do better at praying, everything else falls into line better.
2. Be more realistic. I am not going to get up at 5:30 in the morning and head the gym. But I could, and should, exercise in the afternoons. I am also not likely to spend half an hour a day keeping an insightful journal, but I can jot down some thoughts from my Bible-readings.
3. Create spaces for particular tasks. This is my one solid practical suggestion. For me, this means heading to the library at the divinity school when it's time to get serious about outlining. If I pretend I'm going to study in my apartment, I always find something to distract me. (Perhaps the real point is to take steps to avoid self-deception.)
4. Be hopeful. To the extent that my discipline problem is a sin problem, God is improving me! "Blessed are those who hunger and thirst for righteousness, for they shall be satisfied." (Matthew 5:6) "But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, gentleness, self-control" -- and the Spirit is producing that fruit in me! My sinfulness keeps me from seeing that all the time, but I will, in eternity, be made much more righteous than I can imagine even in my grandest schemes, and that is an encouragement.