I use the Spotone range, which I have had since 1974, five bottles in all.
I use a five zero brush (00000) with which I can do virtually a pin prick size hole.
For larger areas I take my time and do a slightly greyer version first, let it dry, then attack it again, usually the third or fourth coat makes it virtually impossible to see.
I agree with David, a slight moistening does help, the operative word is, slight.
Take your time and don't spot after a session of printing, if you're like me you'll be a bit tired, it is never as well done as when you approach spotting completely fresh.
Mick.