There are some good tips here already, however let me add my two cents as an avid nosebutter enthusiast for years now...
First of all, buttering works best by far with your skis together. Don't even think about separating your legs from eachother the entire time. Your goal is to create 1 virtual "board" that your body leans into and bends, creating a lever action and balance point that you can slide and swing around on, creating the basis of a butter.
Next, you want to make an S carve into the butter, so the first part of the S is an unnatty carve into the second part which is the initiation of the butter as you begin to lean into the ski firmly and swing your upper body into the butter. You should feel your skis loading up in the noses and begin to flex under your weight. (1:18 in the video)
With every butter, now matter how big or small of a spin, the pop happens at 180. Your goal is to confidently swing into a 180 and pop going switch right at 180. The easiest way to pop is to think about swiping your skis back at 180 like backscratcher style. You won't actually fully be able to do that, but if you think of it that way, you should pop correctly. Nosebutter 540's work the best as far as intended physics of this trick. Trying to hold it at 360 doesn't work as fluidly (assuming this is off a knuckle)
Lastly, the thing I never hear people talk about is speed. Going faster will make buttering easier. There are way more forces at work when you are skiing at speed than you on flat trying to bend your skis. They will flex more, your trick will work better and you have a much better chance of landing properly with some speed behind you. You don't need to send it over chads to make it work, but you do need to find a roll over of some sort that will drop away from you and allow you the time to rotate the trick properly.
I linked my most recent skiing here because I do a lot of butters and you can see how I am describing it vs how it looks when I execute it. Feel free to ask any questions and maybe post a video of your attempts if you have any.