I've been playing elemental shaman, and it is slower than I would like but I don't die. There's some good advice above. Don't hold off on using your elemental and ascendance for a special occasion, use them at will, unless you are planning to go after a rare; it's good to have them available then. If fire is down, throw out your earth, it's better than nothing.
When you are full maelstrom, be sure to use your earth shock; when you don't have ascendance up, use your artifact ability. I like to do flame shock, lava burst, artifact and then spam lightning until lava burst is back. Refresh flame shock when it drops.
I don't pull multiples unless i have no choice, and if I think I'm going to pull multiples I like to have ascendance at the ready. I also heal early and often; fights are slower but safer that way.
Hexing is good, I also use thunderstorm? to knock back and frost shock to slow them. You have two interrupts, use them on casters. I think the biggest difference I see with Legion is that fights are harder, so you have to use all the tools in your kit rather than just a couple of dps spells.
All this being said, I'm thinking about trying something different. Maybe I should explore enhancement like Ckemical suggests.