Simmer the brew, don't boil it, such that it doesn't bubble at all but it is on the brink of bubbling. Boiling it extracts more tannins and turns the brew icky by caramelising the sugars in the plant. Strain it while hot, leave to settle then pour off the top, use a tall and narrow container for best separation and make sure to pour slowly.
Also make sure to use an adequate amount of water, if you saturate the solution then some goodies will be lost when leaving to cool/settle, hence why the bottom of the brew has a reputation for being stronger. Using an excess of water also makes it easier to let the mimosa dust settle and pulls out more from the solution.
All in all, experience is the best teacher however. Once you know the ins and outs of brewing it becomes very easy to make a nausea free brew. The method I've described works very well, there is no nausea but it can still bring on a purge, you suddenly start salivating and then it's released which is the way it's meant to be.