There's little things you do that eventually add up and give you the results that you want. Goal-setting is one of those 'little things'.
Having a schedule for your schoolwork makes you organised and time efficient. Knowing exactly what you’re going to study, before you start studying, lifts the burden of having to pick your brains for what you ‘feel’ like studying. It’s less stressful this way and you get to save that five to ten minutes you’d have spent trying to figure out what to do. Plus, there is a certain motivation to stick to your timetable when you work this way, because you will have it in your mind that skipping a day messes up the schedule.
More importantly, you must know how to make said schedule properly. What you do not want to do is put too much in it and then fail to do any of your tasks. Science says we can barely go beyond one hour without losing focus. The time varies for different people. Know what your own time limit is and fix your study sessions in this limit. Note that, like endurance in sport can be increased, so can the time you are able to stay focussed. If you work at it, you can stretch your attention span.
"...commit to getting things done..."
About how much to do in one session, I suggest you do short chapters in one session. Like five to ten pages or so. If the topic for that day is long and challenging, cut it into divisions according to its subheadings. Do one or two divisions in one session. You are not restricted to one session, so you can have a couple of separate sessions, with breaks in between. This way, you can finish the topic in one day, as planned. Putting too much on your plate will overwhelm you. Have you ever picked up a novel, and its thickness made you feel lazy to read it? Same thing happens if you plan to go through many pages.
So set small, realistic goals, so that you do not feel lazy or lose morale because there’s too much to do. And then commit to getting things done.