Set aside a time on specific days of the week, which is allocated to study.
Stick rigidly to those times...never ever skip a session at one of these times.
Do it in this room you're prepareing, and make sure that there are no distractions. Those in the house with you need to know that you can't be disturbed during this time no matter what.
As you have an issue with will power, perhaps best to ensure that you have a treat after your study session. Wether that be some nice food, or a trip down the pub, so be it. But you only get your reward if you do your study. No reward if you start 5 mins late, or finish 5 mins early. (Again enforcing that policy on yourself takes will power.)
After that, it's just about having the discipline to stick to it. There is no easy way.