Been playing for about two weeks, starting out with Tusk. Wondering what scenarios you find yourself using instinct in and how do you optimize it? I tend to only use it to make something safe or when I need to have cancellable moves for armored characters. Thanks!
Go to YouTube and look up Bass’ Rough Sets with DaytonJ. It’s a FT10 btw Bass’ Spinal and Dayton’s Tusk, and Dayton’s use of instinct is really great. He basically uses it to cancel slide->overhead->slide and shenanigans like that. Looked damnably hard to block. 
If you mean in general (since I’m going to assume that you’re new to the game), a great use for Tusk (or anyone’s Instinct for that matter) is to activate it on wakeup. It starts up in 0 frames, recovers instantly, and freezes the screen so you can see what the opponent is doing and prepare your defenses optimally. An example would be that you wakeup and pop Instinct, see the opponent is going for a meaty attack on your wakeup, and input an uppercut/shadow uppercut during the freeze frame so it comes out on the first possible frame.
If you don’t mean in general and need more specific answers, then I’d listen to what @STORM179 said. You can also look up the Tusk reveal stream on the Iron Galaxy YouTube page and they have demonstrations in matches of what his Instinct can be used for.
If you master his instinct juggles, you’ll find that tusk can build up a lot of hard to break damage really quickly, provided he has a bar to cash it out. The downside of doing this is that you burn a lot of your instinct meter, so if they break the combo later on you don’t have a chance to make use of its other benefits such as improved mobility, defense, and mixups. Still, being broken with any consistency is unlikely, because of how effectively he can vary the strengths and timings of his moves.
I usually just use it to make unsafe stuff safe, primarily baiting out shadow counters and then canceling into DP. It also makes his juggles more useful, since he’s no longer restricted to HP after an uppercut.