Yun has always been a character I thought was cool, but I'm so used to shotos and never really played much of him in the little bit of 3rd Strike I've played. What are some of the things an aspiring Yun player should know or always remember to do when playing? Here lately I've been watching a bunch of highlights of Kazunoko's Yun for some things but do you guys have any suggestions?

I'd second @l1ghtn1n's recommendations for the shoryuken Yun subforum, most of that info is still decently useful. Some other basics you should probably focus on would be:

• learn how to link cr.mp into itself and s.mp, as that is your go-to combo in many situations.
• Make sure to hit divekicks low on the opponent, otherwise you will get punished.
• Master lk shoulder into RFC. With this you barely even need to experiment with his super anymore.
• Use divekicks to blowup your opponents long range pokes in the neutral game.
• Mix in non-divekick neutral jumps with divekicks to avoid being predictable.
• Don't abuse lungepunch and ex-lungepunch. They are powerful tools to get into the opponents face, but using them too often leads to getting raw ultra'd or eating a neutral jump into punish combo.
• Learn the follow ups you can do after ultra 1. They are free damage, no reason not to do them.
• Use ex shoulder to get through most mid-range fireballs.

This is all I could think of off the top of my head. Other places in the internet (youtube, shoryuken, etc) will have more detailed advice.

Don't learn Super combos. EX Red Focus after a shoulder is most valuable now.

I will also say don't learn super combos, but then once you feel good with Yun then totally learn super combos so you can style on dudes.

Divekicks are a very powerful thing for Yun, but it's important to recognize that in order for you to use them effectively you need the opponent to be on the ground and mostly stationary, but ideally not thinking about how to stop the divekick. In order to accomplish this you have to make them think that jumping at you or rushing forward will get them hurt, so you need to be reliable at punishing jump ins and using your normals to protect the space in front of you. Once they engage with you in the poking game, trying to use their normals to beat yours that's the time to bring out the divekick. Hit them in the shins and go into a confirm, if they're blocking then either keep up the blockstring for pressure and meter build, bait reversals or go for throws as you think is appropriate.

That's the mentality I used when playing as Yun, and while I don't have much experience I found that my success or failure in any particular match was easy to attribute to either succeeding or failing at some part of this plan.

Before you start jumping around and divekicking like a lunatic, try to just walk forward. The essence of rushing down isn't doing stuff constantly, you just have to make them fear you. So just walk forward and see how they react to being pressured by your presence. If they panic, you are ready to block and know to be careful and bait their crap for big damage. If they try to get more space by teleporting or jumping you will be ready to stop it, which is also good to know for the next knockdown or corner situation. And if they are being patient, that could essentially mean nothing or that they are turtling, either way it opens you up to do whatever you want, which in Yun's case would be lp>lk>mp target combo into shoulder on block combined with tick throws and then shitting all over them on wakeup.

I say this stuff as more of a Cammy player, but it's definitely imporant to establish this dominant ground presence and not only rely on these characters strong air superiority.