Gathering Fire rewards aggressive play. Look to land abilities and basic attacks on your opponent to lower Mantra's cooldown and stay on the offensive.
When using Focused Resolve, slow your opponents with Inner Flame or speed yourself up with Inspire if you're having trouble sticking to a target.
Don't be too conservative with Mantra. Gathering Fire is strongest in teamfights, making it easy to recharge Mantra multiple times.
Karma's passive lowers her Mantra cooldown when she hits enemy champions with abilities and basic attacks. Deny her from getting free hits on you.
Karma's Soulflare erupts for bonus damage in the area in which it's placed. React quickly and escape the circle to avoid taking heavy damage.
Focused Resolve is a strong disengage tool. Create distance to avoid being rooted and seek to engage afterwards.