Kissing a girl for the first time is a very exciting step and the most difficult thing is not how to physically kiss a girl, but how to come to a kiss in general.
If you already have a relationship with a girl, you know that she likes, then it is important to choose a good time to kiss. Ideally, if this is an intimate, you sit, stand, or lie nearby. Usually it is enough to look this person in the eye and remain silent for three seconds and slowly reach for her lips.
The girl will react as well and reach out to meet you. If this option seems difficult, then you can contest at what you are sure of and choose a prize in winning an contest - her kiss, then the girl will have to kiss you on her own.