Let’s start with A site.
The most important thing is to throw a grenade into the middle of the site. It will be effective for a quick rush, or when you get Spike planted, but the defenders have retaken the plant, so you should use a grenade.
Use your second Killjoy’s grenade on the ‘electric’, because the enemy is often hiding there.
You should throw the third grenade on the ‘Nine’ if the attackers pushing up the Mid and entering the Haven.
Killjoy on B site
Use your first grenade into the connector (exit from the mid lane)
Use your second and third Killjoy’s grenade into the exit of the forest.
Throw your fourth grenade into the middle of the forest behind the wall.
Use your fifth grenade into the middle of the Plant.
All of these grenades are effective when retaking a bomb site or slow pushing. Play Valorant. See you on the battlefield.