There is nothing other than practicing Self-Discipline to manage this.
Isolate yourself in a room with Book to study, Notebook to take notes in, Pen/Pencil. No Music/TV/White Noise/Distractions etc. It is just you and the subject to be studied. Set yourself a Functional unit of study (say a complete chapter) and fixed amount of Time(say 30-mins to 1-Hour) to do it in before you take a break. This is key. Your Mind will take some time (say 10-15 mins) to calm/settle down so you have to persevere. That is where taking Notes (eg. Cornell Note-taking method) comes in handy. It helps your Mind gradually Focus on the subject matter by involving your entire organism through the process of active Writing. You can also read out aloud along with the above. Another Technique to help your Mind Focus is to invent a ritual to do explicitly only before starting a study session. The Mind works contextually and hence once trained with a specific ritual before a study session will automatically switch to that state on encountering the ritual. This is the formation of a "Habit"; and Self-Discipline is the key.
Sounds like a holistic question: depends on what is happening with you and the causes of the distraction. For example if you do 60h work weeks then maybe you simply are too tired.
