So first of all. Retaking sites requires practice, especially if you are playing at a high level. As you might know there are different positions that Ts can hold in a site, and different entry ways that CTs can attempt a retake from.
As a CT:
By retaking what you realise first is that when entering you will be exposed to a number of angles, by practicing you can learn to use utility to disable some angles while checking others and making your way into the site without getting in 1vx situations eventhough there are 3 Ts in the site. Other than that, you also practice your movement. Moving well will close off angles very quickly, for example when retaking B in mirage through short, after clearing close angles, you should swing hard right in order to go past the bench angle where a T could be holding with awp (also apps).
So as you can see little details make the difference and you definitely need to practice these things and improve. You learn where to preaim where to prefire, where to run and where to walk. You learn flashes, mollies, smokes. Common nade positions like truck in B. etc etc.
As a T:
You learn how to hold the site. Now eventhough people dont always communicate in retakes, simply by looking at the map you should immediately know what angles are being held and how well they are being held, so you can decide quickly what to hold and from where. Secondly you learn to use your utility efficiently. For example if again you are holding B in mirage, it might not be immediately necessary to smoke short without confirmation that a CT is indeed attempting to retake there. You learn where to hold and if you feel pinned how to get out. You develop gamesense and timing during the push so you can do the insane stuff you see in frag movies where people win 1v4. etc etc.
This is something 95% of the cs community dont understand because they are too busy running with p90 and thinking they are good because the get 30 frags against noobs. Cs is 10% aim and 90% gamesense, knowledge, movement, timing, execution. And most of these people attribute this 90% part to luck or cheats. Where in fact it is the biggest aspect of the game and you are completely disregarding it.
So after reading all of this, get gud, and stop making threads about these things when you have 900 hrs and are gold nova 1. This is not an insult, just a fact. Im not telling sebastian vettel that its stupid to walk the racing track with his crew before the race because he has state of the art simulators that help him memorize everything about the track.