Focus on what exactly? If it’s just focusing on a task in general, remove distractions. If you catch yourself doing something unnecessary when you have a task to do, immediately force yourself to stop and focus on the task needed to be complete.
Make studying fun! I don’t know how you study but I would say the more appealing studying is the better chance you have of focusing. Like decorating your notebooks or write your latest knowledge on sticky notes to stick all over your room or something. Just make it creative and engaging is all I’ll say!
You might find the Pomodoro Technique useful. It's basically dividing work/study time into intervals with short rest in between each one. You can read more about it online. I use it when I do listening exercises, because I get distracted quickly, so I force myself through 5-10 minutes of absolute concentration and then rest for a couple of minutes. Then repeat the cycle as many times as needed.
