A lot of it is universal advice for all dps like being aware of your ogcd cooldowns and only double weaving certain things. The biggest thing is not only knowing your skills and what they do, but learning the fight so you can maximize uptime and know when the best time to use them. Ninja being a support role knowing when to assist with enmity management, throwing smokescreen on a healer or dps gaining too much hate or using shadewalker on a large pull right before you start to aoe are things that aren't done enough as a whole.

Tailoring your role actions to the duty you are doing will help as well, bringing low blow to stun if you are going to need to, goad on a tank or dps that is low or was just raised, or feint if a boss has psychical damage tankbuster to aid in mitigation is huge. Personally i see no need to ever really have true north , but there are arguments supporting it. Ninja has 3 positionals that need to be hit, aeolian edge, armor crush, and trick attack. We were hitting all of these easily for years before true north was a thing, so i don't see the need to take it when i can have a more useful skill instead.

Trick attack should be used on cooldown during a boss fight, followed by dream within a dream once you get it at lvl 60, ideally you want to line it up with your teammates ogcds whenever possible, battle litany for drg, embolden for rdm, ect so if you have to hold it for a few seconds before you use it for that then do it. Also try to apply suiton within the last 10 sec of trick attack's cooldown so you can hit it as soon as it comes up and not have to do a 3 step mudra right before.