Once you get used to it, it shouldn't be that bad. Just don't over do it. Your body will associate 'the sickness' if you get it with the Rift itself before doing anything. Like if you get sick of Tequila it's hard to smell it after that for a while.
Do some of the calmer demos, get your VR legs. Cockpit experiences are the best. Racing sims (Assetto Corsa, Euro Truck) and of course ED.
Also, if you can a little desk fan helps, the wind can prevent fogging and such. I believe mine is because for some reason breathing through my nose somehow goes 'up' and fogs up one of the lenses. I've since put a little cloth in there and it hasn't happened since.
Also, get that program that switches displays here:
https://forums.frontier.co.uk/showthread.php?t=65258
It has a color changer and green is the best because of the screen type used in the DK2.
I do get vertigo every now and then. When you launch and then turn your ship 'down' to point at the pad it still "feels" like I should fall out of my chair, lol. Just take it in stride, take it off immediately if you start feeling a little woozy, don't push it.
I can go for an hour or so but then it just kind of doesn't feel that great on my face. Plus I can't really be "immersed" in a game for that long with so many other distractions around the house sadly.