I started with my girls spending time with just my hands in the cage, inspecting things.. turning stuff over.. and if they ever came up to me 'oh look, coriander and dandelions!'.. I would take the time whilst they were nibbling whatever I was holding to tickle an ear, or stroke the shoulder blade with a finger from the same hand.. Dont go for the face, neck or paws straight away, these take a bit more time.. shoulder and back is the area most guineas groom each other but hips and tummy are a bit more sensative for them.
I ended up coaxing them in the tunnel and lifting it out.. took a few months (and I was still doing it every once in a while a few years later). One of my girls got used to running up to the front of the cage when I presented food. It didnt take long before I was scooping her up as she ran to the front of the cage and reached up to see what I had.
Only ever got used to getting out one of them, the other never liked it. Good luck! and remember coriander and dandelions are a slaves best friend!