I decided to write a list of VR tips because so many creators don't necessarily have access to VR yet. These are guidelines, things that the VR community has learned over the past few years through trial and error. There are successful games & experiences that don't do these things, but that doesn't mean that you shouldn't take these things into consideration :)
Avoiding Motion sickness:
1) Optimize to run at 90 fps in a VR headset: This means being conscious of triangle count, texture sizes, draw calls, script efficiency, etc...This will require testing, I am happy to help anyone who needs a tester with a headset and I am sure others will too.
2) Don't move the player: Let them control their own movement and "camera" through walking and teleporting. But many experiences will want to do this, so go to tip 3 and 4 :p
3) Restrict their vision during movement: If you are going to fly or drive someone around, it seems to bother people less when their field of view is small. You can do this by putting a helmet on or enclosing them in a vehicle. Or you can just cover most of their screen with black except for a small area in the middle while they are in motion.
4) Avoid acceleration and unpredictable movement: So make them go full speed instantly instead of easing the animation and make the movement straight and/or very predictable. This won't work for a roller coaster, but you could make a commuter train that follows that suggestion easily.
5) Provide alternative transportation: A player can just choose not to play on a fair ride, but they NEED to get around your experience. If your experience requires a player to do something like ride a sail boat to get to another area, provide another means of transport for your VR players so they are not forced to feel sick to get to your store. Maybe a teleport pad or an enclosed submarine :)
6) Try to avoid moving horizons: If for example, your player is on a teeny tiny island surrounded by stormy seas or in a clearing surrounded by trees that are swaying like crazy in the window, they will probably feel sick. Again, you can avoid this, my making sure that vistas like that are not filling the majority of the player's view.
7) Keep ground level where possible: VR players know they will need to teleport around to go hiking or dungeon crawling. But in situations where they are still, like around a fire or in a store, the ground should be level so they can walk around their play spaces to enjoy your experience. Right now, if the player steps on a raised brick or small slope, their headset will unexpectedly move up in the world, even though the player only felt level ground in the real world and never noticed the obstacle in VR. So to them, it is just disorienting and it can make them feel ill.
8) Go easy on collision: Unexpectedly walking into a collider around a rock and then being teleported up on top of it in VR is again disorienting and unpleasant. And the player only sees the actual geo, not where the collider cage is. Also, players in VR tend to just avoid solid looking objects on their own. We are conditioned to not walk into rocks and tables. You do need colliders for many things, just keep it in mind when you are designing.
Delighting your VR player & keeping their experience positive:
1) If it looks interactive, it should be: Games decorate with switches and small objects all the time, but it is crazy frustrating as a VR player to see a light switch and not be able to flick it. Or see a stuffed animal and not be able to pick it up. Try to make it obvious at a glance what is interactive in your scene to keep your player happy. (Also, light switches are fun in vr :p)
2) VR players have a personal bubble: Don't make the player stand too close to an NPC or another player. It feels just as weird as it does in the real world. Though something like a vampire game could have tons of fun with this, making the player get close and "bite" an NPC would be hilarious. But if they are just trying to talk to a shopkeeper, they shouldn't have to stand any closer than they would in reality.
3) VR visitors are not restricted in their viewpoint: They can crawl under objects, peek around things, look up from under stuff. Make sure your world is solid and try to avoid weird cheats with transparent flat objects when you can. They don't look very good in vr. It is generally better to have chunkier detail that feels "real" than many flat planes with baked images.
4) Scale should generally be correct to real life: This means that if it is a normal house, then the chairs, doors, tables should be the size they would be in reality, not scaled up to look good for the 2d view. The upside is that a huge statue/dragon/castle/monument actually feels giant and impressive in vr!
5) Playing with scale deliberately is fun: Making the player a giant who lives on a beanstalk towering over a city, or building a tiny village fairies in a mushroom town will both be super appealing.
6) Small cozy spaces & sitting on the floor are often appealing: Getting a camera into a pop tent in a traditional game is a challenge, but a VR player can easily go into a space like that. Though you should consider accessibility since a player might be in a wheelchair or have other mobility issues, and claustrophobia is another consideration in VR.
7) Particles can be really amazing in VR: I don't know why, but they tend to feel quite magical. I prefer the 3d ones, but even 2d particles can add a lot of pleasure to an experience.
8) "Eating" in VR is hilarious and fun: If you make food, you can bet the player will put it up to their mouth to pretend to eat it. If a bit then disappears from the food, they will continue and eat more.
9) If it can be thrown, it will be: I have seen this in every possible game type. Make sure that if a player really really needs an item, there is a way to get it back if they throw it away, lol.
10) Multiplayer is amazing: Giving players an excuse to interact with each other in positive ways can't be underestimated. Being inside a social space in VR feels really good, so you want them to stick around together. It will make you experience that much more special.
Pushing the boundaries is fun, and it should be done. But enjoying the special things that your medium (or game engine) can do well is worth doing too. VR does put some constraints into place, especially on movement and framerate. In some cases, this may mean you have to design slightly different spaces for your VR & traditional players.
But VR is a space where you can make someone kiss a toad to progress (and they will feel so dumb doing it), where they may feel actual fear walking across your scary rope bridge, where violence might make them feel queasy, and they will have actual memories of your experience being a sort of "real" place to them. Horror experiences can be terrifying, live performances and dancing can be epic. And multiplayer competitive games are really fun.
I know a lot of creators are feeling sorta turned off by the design decisions that have to be made to make VR work well, but the impact you have on the visitors in VR can be amazing. If possible, find a friend with a Vive or Oculus Touch and visit your experience. Standing inside a world you created is hard to describe but well worth it :)
Hope this helps and sorry it was so long!
If anyone needs their experience tested in VR, I am more than happy to. Though I will be very direct about performance-related feedback. I want first time VR users in Sansar to feel great. You can request testing or ask questions in the #vrtesting slack channel :)