What directives to start with?

So I've got to challenging and can face tank most - but heroic is still out of reach for now as I need to practice more cover to cover etc.

In the meantime, what order should I set the directives that will be a more gradual increase in difficulty?

I don't know how you guys do legendary - I shoot them and their armour doesn't even budge - I must have a pea shooter 🤣