First of all: take a break sometimes! You are just not able to concentrate for more than an hour. You will need a break! The second thing that helps me from going on my phone is the app Forest. You set a timer for how long you want to concentrate and then you plant a tree. If you go on your phone, the tree will die. But if you leave your phone alone the tree will eventually grow! The last important thing is to set clear and reachable goals. For example, if you have to read a book for english, don’t just put ‘read’ on your to do-list but put ‘read 20 pages’ so the goal is clearer. It’s also important to set goals that are reachable. When your goals are too big to reach you will probably be less motivated to work. The last tip is to grab a drink and a snack while working. When you are working, while enjoying a snack, you will be more concentrated because working becomes fun!
There's an app called Forest that might help? You set timers and during that time you grow a tree (or bush). If you get distracted and use your phone for something else, the tree dies! I've found it really useful.
Perhaps treat concentration like a muscle. Exercise it. Start small and increase gradually. Example: pick a task that usually seems mundane; set a one minute timer, and for that minute focus on that task. When the timer is up, put it aside. Do this every day or a couple of times a day. When one minute seems like nothing-it’s easy, increase your time to 1.5 or two minutes (don’t jump too high to quickly). Continue this. Even though you are focusing on one task, I believe this skill of focus will spill over into other areas…maybe without you even noticing that your concentration is better!
I concentrate better when I either make the task fun, give it a deadline or when I have enough rest. I tend to daydream more when I'm tired. But if my task has a quick deadline for example "i have half an hour to finish this task"and I time myself or if I make it more fun and engaging then it's easier to focus on it even if I'm tired.