1. Get someone to keep you accountable
I personally use Habitica (I recommend checking out) and have a friend that keeps me accountable
2. The Pomodoro method (as mentioned before) is really useful for building effective study habits. Why? Although it consists of a 25 minutes of concentrated study and a 5 minute break, it can really help you get started on your task and overcome that original procrastination. After several sessions, you may reward yourself with something. Maybe an episode of something on Netflix.
3. Get rid of all distractions before studying.
I cannot stress the benefits that you will receive if you place your phone and laptop out of the room. If you need your laptop to work, I would download Cold Turkey Blocker which allows you to block certain websites for a period of time.
4. Find a good study environment
You might want to dedicate a space inside your house to study. Studying in a place where you procrastinate will inevitably end up in well.. procrastination. If there is no space, I would go to a library/cafe, whatever suits you. Personally, the library suits me because the sheer amount of people working/studying motivates me.
5. Set Goals (as DrDusk mentioned)
Create short term and long term goals you want to achieve. This will give your study a sense of direction. Do you have an ATAR goal? Write it down and stick in on your wall.
In light of all this, I know its simply unrealistic to just start following all of these steps. I would recommend really capitalising on the Summer Holidays to develop consistent study habits. It may seem a bit daunting at first but we all had to start from square one.
I hope I answered your question. If you have any more feel free to PM me