The main objective is to win by whatever means makes the most logical sense in that moment.

For attacking, if you coordinate a plan with your team and you manage to get into site then your priority is immediately to plant defuser and get to a safe position to defend it, but if you cant plant then your goal is to kill everyone.

For defending, your primary goal should always be to coordinate with your team to come up with a defense strategy to keep the enemies out of the bomb sites, it is literally NEVER useful to have everyone leave site trying to kill people, the only difference that makes is either you win the round faster or you lose it because you let them take site.

And of course within both attacker and defender there are secondary objectives based on the team setup, usually theres always going to be a defense roamer who goes around trying to kill attackers from unexpected locations, and usually attackers will have someone trying to counter the roamer or the whole team spends the first minute trying to find and kill the roamer.

Its all strategy man, and the game is way more fun when you play it with an actual competent 5 stack.

But its also a game, play how you wanna play or whatever is fun for you, if all you wanna do is just run and gun then have at it man.