Askmen.com has an interesting article about how to improve oral sex. My girl is always willing to participate, but here are some tips that may help you out.
The most important thing you can do to make her more comfortable exploring your nether regions with her tongue is to clean yourself up. You may have had a shower in the morning, but by the time the evening rolls around you’ve likely used the bathroom a few times and perspired a bit, so it probably doesn’t smell or taste very good down there. For a longer and more enthusiastic oral sex session, make a point of washing up right before it begins. To avoid spoiling the mood, you could incorporate a mutual bath or shower into your foreplay.
The majority of women prefer not to swallow semen, but your girlfriend may be persuaded if you make an effort to make your spunk taste better. A vegetarian diet is the best way to make your taste milder. If you’re not ready to go meatless, try eating foods like kiwi, watermelon, pineapple, and celery to lighten the taste. Make your semen taste sweeter by incorporating plums, blueberries and cranberries into your diet. Beer and coffee will make you taste bitter and dairy products can produce putrid tastes.
Some interesting advice here. Check it out.