I don't know if anyone else does this, but when I buy a plugin, or a VST I make sure I teach myself what it does, and how I can use it.
I don't always NEED the plugin, but occasionally I take a punt, which nearly always works out well,
Trust your ears (for me the sound of Izotope stuff just doesn't do it for me, except the free imager) not your eyes, there are a lot of wonderful looking plugins out there, but your listener won't see those wonderful recreations of old analogue gear.
1. Try them first, most can be trialled for a couple of weeks for free.
2. Read the manual, understand what it says, there have been some where frankly I have no idea what they are saying (Kirnu Cream)
3. Create a test environment, usually separate Lead Vocal, drums, guitar and keys, then apply it to that and see how I can use it. Pick instruments that you are very familiar with their sound, your old acoustic guitar for example, so you know what the plugin is doing to it.
4. Watch some product videos, usually from the manufacturer, and well regarded reviews.
5. Try out the factory presets
6. Try extreme values.
7. Try it on an old song
8. If you find a particular bunch of settings you like, save it as a preset, in an orderly way, use a naming convention always helps.
Some of these things are very complex and have a lot of
subtle differences between settings, take the Abbey Road Plates... I saw
@pompeyjazz use this, and so I checked it out, and by golly it's brilliant, but there are so many permutations...so I saved a few of my favourite settings as presets and I tend to use them over the presets.
If theY are really good then I'll build them into my DAW templates.
Like playing an instrument, plugins do need practise, they can leave one's tidy creation in tatters if they are misused.
...finally, just because you've bought it, and it's new, if your track sounds great, then don't use it.
as always, hope this helps
Rich