Some really good practical tips there from Diesel and DegD.
My number one tip is to come up with a style you are happy with that doesn't involve a totally exposed hairline. I don't mean you shouldn't aim to have a good-looking undetectable hairline, but achieving that is something that many newbies struggle with at the start, and if you are trying to keep your switch to a system on the down low why make your life more difficult and edgy than it needs to be? Even for experienced wearers, the hairline is still the #1 place where a hair system can look detectable. There are plenty of good looking styles with a covered or partially covered hairline. I personally like a style where you brush the hair forward at the front and flick it up with a bit of paste - the hairline is visible, but always in the shade of the hair.
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I find that gives me a bit of cover just in case anything goes wrong, like a little bit of lace coming adrift.
I like argan oil as a product, because it seems to soak into the hair and/or evaporate, so it doesn't make the hair heavy like some other products.