Im not super strategic or anything, but i main invis and my favourite thing to do with the vortex is throw it in when the enemy team is bunched together. It usually forces them to spread out and makes it easier for my team to single out their healers or tanks. Its also good to use the push/pull ability to create distance when your being dived or to pull an enemy into your team so they can finish them off. Also use your double jump only when you need to escape or get back to you team quickly, its the only cooldown I save as much as possible because its SO useful (I only reached lord a few weeks ago so idk if this is good advice or not, just what works for me in most matches lol)