1) Emotional Connection: Women are stimulated a great deal by a strong emotional connection with their partner. While men are more aesthetically sensitive, and react to things they see, women are more turned on by what they feel. The first step to satisfying your girlfriend actually occurs outside of the bedroom; being emotionally available, in-tune with how she's feeling, and attentive to her needs will make her want you more than ever. Simply knowing how much you care and are committed will provide her a high level of stimulation that will ease any sexual interaction.
2) Compliment Her: Women (and men) tend to be somewhat self-conscious and insecure. Even if we're not willing to admit it, hearing that we look sexy and appealing to our partners will help to make us more inclined to want to be sexually engaged with our partners. Often times, once we're deep into a relationship, we take those comments for granted, and forget to tell our partners how attractive we find them. Even if you're saying it to yourself, make sure that you tell your girlfriend how beautiful she is; you'll help her to feel sexier, and you'll see the effects in her upped desire to get under the covers with you.
3) Foreplay First: My boyfriend and I have recognized the fact that foreplay is critical to eventual orgasmic success. I personally love to go down on him, and seeing him get hard and knowing that I'm turning him on gets me hot. Guys--you don't have to be super dominant, but don't be afraid to ask your girl to touch you or to give you a little bit of head; she'll love the fact that she can get you going! Before you go in for it, make sure that you also pay your girlfriend some attention. My boyfriend does this amazing thing where he lays beside me and touches me to get me really wet. When I'm getting close to orgasming for the first time (yes, he makes me cum more than once), he puts himself inside of me, staying on my side. From this angle he can touch me and be inside of me at the same time, which makes me just go crazy. This benefits him as well, as once I've cum the first time I'm extra lubed up, and then we can focus on him.
4) Whisper Sweet Nothings: Again, your girlfriend will be turned on by the idea that you are hot for her. It may seem obvious as you're going at it, but reminding her during the act will stimulate her even more. My boyfriend says things like "I can't wait to be inside you," and "You feel so good." While this may seem simple, these little comments make me even more hot than I already am. As women, we want to feel wanted, and when we know that our man is really into us, it makes us even more aroused than we already are.
5) Cuddle Her: After sex, fight the urge to pass out immediately, and give your girlfriend a few minutes of affection. If you came hard and if the sex was really good, tell her! You'll increase her sexual confidence, and make her feel great about your experience. You may feel as though you're doing a lot of reassuring, and that's because you are! Go with it though; it will do more than you know.
After engaging all of these techniques, go out on a limb and ASK your girlfriend what she wants. Much of the reason that my boyfriend and I are as successful as we are is because we talk and communicate. We constantly revise what's working and what's not, and by staying on the same page, we're able to make our sex better and better each time out. Don't simply settle for what you're experiencing, even if it's "good." The last important factor contributing to your success will be constantly seeking that ability to be "great." Happy sexing!