You first have to mutually know that you aren't going to go further than you are comfortable which is going to mean openly discussing your intentions with each other. It will take conviction to stick to your personal boundaries, but if you both respect each other you should be good. As for when, maybe before you say goodbye after a date, but make sure it's at the door or somewhere where going further would take more maneuvering giving you time to think about what you're doing. If one or both of you don't think you can show restraint, maybe stick to public outings where going further is not an option.
It's just a kiss. If you like him do it. You're not having sex. Plus you need to kiss, if he's not the one, at least when you find the one you will know how to kiss very well :). But this rule doesn't go for anything other then kissing lol