Have you read the Tsundere Imouto guide?
https://docs.google.com/document/d/1...y0TrCa0qg/edit

It has basically everything you need to know. It's a bit complicated to reply to your post, because as said in the guide SMN relies on managing several "mini-games" so it's about optimizing each one of these.
Keep your DoTs up, cast ruin 3 a lot, ruin 4 when it procs, DWT makes moving easy, get as many Wyrmwaves as possible out of bahamut, don't clip...
Enjoy!