The biggest mistake lower-Elo Terrorist teams make is rushing 5 players into a single chokepoint every round. This allows the CTs to rotate freely and stack the site. Instead, you need to play a "Default."
What is a Default? A default means spreading your team across the map at the start of the round (e.g., 2 players towards A, 1 in Mid, 2 towards B).
The Goal: You are not trying to plant the bomb yet. You are safely taking map space, listening for CT utility, and waiting for a CT to make an aggressive mistake.
Once you get an opening kill or find a weakness, the Lurkers rotate to group up with the entry fraggers, and you execute on the weakened site.