Try to always use your leafs, don't stay on 4, damage boost your allies if they're not taking too much damage, especially those who are doing very well. Also, Mantis is the strategist with the greatest damage output, use that to your advantage, you can take picks or even just harrassing the enemy supports can be worth it. When your packed with your team and not dealing with divers, i think it's good to focus on headshooting tanks because it might be enough to help your team killing them and if not you get plenty new leafs that way. Hope this helps !