Pretty much this... Just grab her firmly (but not to make it uncomfortable for her), get nice and close and let the instinct take over.
I smell a troll, but lemme post this anyways. I assume you're new to these... real-life treats. If you got any female friends (or basically anyone) who could teach you how to kiss, you'd best take the course. If you do not, there are some general mistakes you want to avoid
- mouth wide open - don't do that. That's a phase you'll (maybe) get to later during the actual kissing. You don't start with it unless you want to make the impression you're going to swallow her whole or make your face look like that of a fish
- swallow your saliva before starting the kissing - for real, I've met so many girls that would leave my face half covered in their saliva... feeling like a sucked lollipop is only funny for the first time. Also don't be afraid to interrupt the kissing just to ninja swallow... You don't want your lips to be wet from your saliva (tends to get sticky and doesn't smell good once dry), but I've found a lip balm to be quite useful for extended kissing sessions!
- the tongue - you do not want to stick your tongue all the way down her mouth and throat. Although I've met a girl that did this and liked this, I've found this intrusive type of kissing very uncomfortable. General rule is you do not want to go beyond the 'boundaries' of your own mouth... You'd both just kinda meet 'in the middle' and figure the rest out yourselves...
- eyes opened or closed? - well I recommend just narrowing your eyes until your lips touch and close em after. You don't wanna headbutt yourselves just coz you both had eyes closed. But having eyes wide open during the kissing itself may be considered rude/unpersonal.
- breath - unless you're having some dental related issues, a chewing gum will sort out your breath and taste... (you generally don't wanna kiss someone without the gum unless you're willing to accept the option of never getting to kiss the person again
)
I think that's about it... there are many styles to kissing besides these basics but you'll figure out what style is your girlfriend using and just synchronize later...
edit: added some details...