For discipline to be successful, each step in the journey must be attainable. If we have a target to read a biography of Abraham Lincoln, but we don't even read the newspaper, we will get very aggravated! Each step along the journey to our target must be attainable.
If I need to read my bible more (not even a specific target), I shouldn't adopt a goal to read the New Testament in 30 days. That's kamikaze work right there! If I don't currently exercise, I shouldn't set a target to exercise 5 days a week for 1 hour.
Any discipline I select must start with attainable steps or I'll get aggravated and give up. Start by exercising 3 times a week, read your Bible 10 minutes a day, 3 times a week, etc. What small steps can you take right now that are attainable? Adopt these and then see what happens!