how can i improve in my weak subjects

Wake up a half hour earlier and spend that time reading from your textbook. If you’ve already read the chapters, spend the time rewriting the key concepts into a notebook. A half-hour out of your day in the morning probably won’t create a huge impact on your schedule,

Practice and you will improve. In best case develop passion for your subjects. This eases up everything.

Need to learn the basic and fin the flaw. And make the subject interesting while learning.

work hard, that's what is important. Practice makes a man perfect.
keep on practicing the subjects which you feel hard, surely it will give you success

A subject in which you are weak , normally the reason could be you don't have much interest in such subjects , if you will your complete concentration in that subject only that is also not good.

so my advice is you give your 1 hour daily to that subject at any cost and also try for some other option apart of reading the books for that particular subject you try listening the audios or practically try to learn the lessons or topics which will always help you to understand the subject in better manner.

I will suggest you to first of all clear this fact from your mind that this is your weak subject. Start it as if it is something you are not comfortable with and not something that could be considered as a weak subject.
Now the next step is how to break this discomfort. From my personal experience, in my childhood, I had the same feeling about science until one day when I was exposed to its fascination. I mean, science is amazing in a sense that it gives you a reason to all the happenings around you. In my childhood, I remember, my elder sister introduced me to science magazines and science fiction stories which amazed me with their scientific logic behind them.
I will suggest you to read such comics or short stories which will bring you closer to the fascinating world of science.
To start with, I will suggest you to read H.G.Well's stories like "Time Machine" and "The Invisible Man".
Believe me, even if you are not willing to pursue a career in Science still its a worth subject in understanding your surroundings.

Well, even I thought I was weak in studies and even I think like that even now. I'm trying to get over it. Well, let me explain. Nobody is smart or dumb in this world. It all depends on the interest in that area and hard work you put in. How much effort are you putting ? List out your stronger and weaker areas. There could be a situation like you are weak in a subject just because you don't like that subject. I used to think I'm weak in maths till my 6th standard. But when I started liking it, I came to know I was actually good at it. So, my point is, check your efforts and constantly try to improve your grade. Today should be better than yesterday and so on. Good luck !

First take off from your mind you are weak in any subjects. you may be slow in learning but all you need to do is you should be confident that you can learn anything. If anything finds difficult you can opt for extra tuition for that subject and seek advise from them.