Mainly to all girls, How to ask my gf if she's ready?

Me and my gf have only really gotten to kissing on the lips. I want to let her know that I want to have s(e)x but ONLY when she's ready. What everyone tells me is 'joke around with her' like first start kissing her on the neck / above . After thats done start snuggling with her (like when watching movie) then touch her s etc. Basically what im asking is after were comfortable with kissing on the neck etc. what should come next? All help is appreciated thanks!