ok heres the basics, my routine, for hairline ,the same for the scalp except you don't need to be (too pedantic with anything behind the hairline.)

1) golden rules---------clean and dry.!!!!!!!!make sure you've removed all the adhesive, use you're finger nail, its a great tool but be gentle.
try sellotape on the area just avoid placing it on the hairs.

2) apply one layer of adhesive, I love orwg, oil res white glue, time it!! don't guess it, leave around 10 mins up to 14, until its dried clear.
then fold down the lifted hairline skin, or lace onto it, if you've cracked it it should look seamless, transparent and look amazing.and strong as hell.

I spray a deodorant to block or hold bak sweat release , "pro touch" optional

its more difficult in the summer, so if you can use a fan, a bigg fan.

ps! wash youre hands before applying or smearing adhesive as youre fingers may still have natural oils on them.

you don't get it perfect first time, but practice makes not perfect but pretty close to it

hope this helps
aanthony uk

its worrying at first, but as the saying goes once you know how, and get into a routine. Then finly tune the routine