I don't get any idea on how to choose a problem that could teach you some concept. Recently I am struggling with 1100 rated problems. I am usually not able to solve any question of this category during the contest. By applying tags is also not helping me. What should I do next in order to improve??
A way to practice competitive programming
Rather than only focusing on solving more problems understanding you should try to analyse your own solution if you have even a small doubt about your code. This way you can apply that idea later. Knowing something vaguely may help you solve one problem but you might get stuck on another problem based on similar idea.
Also checkout other people's approach, you might get some better way of implementing what you did or you might learn something new.
If you feel like you really a roadmap so can get a small push then you can checkout this video from galen_colin
From Beginner to Grandmaster — Complete Roadmap for Competitive Programming.
Hope you surpass your limits and enjoy CP even more :)