Even though it's possible to create some out-of-this-world coasters in Planet Coaster, your visitors will always prefer something more realistic than 60ft sheer drops and tracks that inexplicably take them underwater. When you're testing each new rollercoaster, you're going to want to ensure that at least two of your ratings are green to maximize each ride's profitability.
Though it may be tempting to create a crazy coaster and ignore the test results informing you that there's a high likelihood your guests will vomit after experiencing it, instead look at altering the parts of your ride in which the three meters veer into the dangerous red territory, and replace those parts of the track with sections that put on the brakes and slow down the car's momentum.
If you want to create a rollercoaster with less jarring motions, something which can prove to be off-putting for most guests, then you're going to need to focus on the angles of each turn your ride takes. Jolting those riding it from left to right on a whim is a surefire way to up that nausea meter, so you're going to want to ease your guests through each turn it makes. You can do this by way of angling each track into a bend -- for instance, if you're taking a left turn, angle the track from 23 degrees into 45 degrees left, then straighten it out at the next available opportunity. It's also important that you don't cram in too many loops or rolls, as doing so can prove to be disorientating for those riding the coaster. If you focus upon creating an exciting rollercoaster that doesn't make your guests want to barf, then you'll ensure that they'll rake you in as much cash as possible.