First, make sure both of you are comfortable with the prospect of kissing each other. Some girls are very attracted to the idea of kissing, and some simply are not. If a girl is not willing to kiss you, the best idea is to respect her wishes and let things lie for a while. Consider asking friends of hers whether she has ever mentioned wanting to kiss you or if they personally think that she would be open to the idea as they probably hear her talk about you more.
If you joke around a lot, then it may be appropriate to ask her outright. Laugh as you say whatever you are planning to say and then be prepared to say 'Oh, I was just joking, you're special to me whether our relationship is physical or not,' or something similar.
Remember, location is key. If it is her first kiss, she may want it to be somewhere with sentimental value or have some other preference to where she kisses you. Be prepared to accept whatever she says as it may be more special to her.
If she does, just go for the kiss and make it a special one.
Don't have your hands all over the place, be appropriate with where you put them.
Don't purse your lips (this is a different kiss)wait until both of your lips are almost touching then close your eyes and go in for the kill (but not too strong most girls hate it when you push hard on them (unless they like to play rough!!!)
Make sure you both are very attracted to each other; otherwise, one person may feel hurt or used.
Make sure that you are in a reasonable place to kiss someone- if she's a shy girl, she probably will not like it if you try to kiss her in the middle of a roomful of people. Around parents? No way! Remember: Location is key.
Do not forget or neglect basic personal hygiene (i.e., the use of deodorant, chapstick, cologne, etc.) when you are planning to kiss your girlfriend- otherwise, she may simply be revolted by you and refuse to let you get too close to her.
Brush your teeth or chew mints for the same reason- girls do not like kissing boys who taste like garbage cans.
It does not mean from kissing you are going straight to bed so, be careful you can tell when she is kissing you softly or passionately.
If you have long hair keep it out of your face! No one likes the taste of hair in their mouth!!! Gross!!!
Make sure you are both comfortable with it!!! And don't try to push her into doing something she doesn't want to do!!!
When you are finished with the kiss, smile, so it doesn't look like they did something bad (even if they are a bad kisser!!!) if they liked it they will most likely go for more!!!!
Go ahead and do this back!!
Do not be pushy or forceful when kissing your girlfriend. If she does not want to kiss you in the first place and force is required, chances are that the kiss is not going to be a very pleasant one.
Do not rush kissing, it should be taken in a timely manner.
Do not get too cocky or go too far, especially on a first kiss.
Do not put on too much cologne!!! It will make it way too strong and she will definitely not want to kiss you then!!!
Do not go for it if she isn't comfortable with it, yet remember time is of the essence!!!