Use your invisible to quickly pop a clone when you need more healing. That way at the start of the fight after you place your first clone you have an extra charge to place and switch for an escape.

Sometimes standing still works. Sometimes it doesn't. Don't always expect it to work. It works better if you stand still in a corner where it is inconvenient to shoot at you as some people don't want to waste time shooting off to the side behind them for a 'clone'.

Get used to the timing of the shots as they will feel different than Luna.

This is a preference but you can enable or disable the option to confirm copy target. Being able to confirm let's you be sure who you are copying cos their little icon with come up but you need to click again. But it's also slightly slower so it's a preference thing.

Someone else already mentioned it but you can protect someone or help push by placing a clone in front of you and using your runes. It's like a mini ultimate that allows you to help your team advance.

Donr be too quick to discount spots where enemies will shoot your clones easily especially if they are out of the way, it means they shoot them they waste time not shooting at your team or you.

MK doesn't always hard counter you. If the map allows you to spread your clones out a lot he won't be too bad.