the thing about sex regardless of if its same sex or not is knowing your partner and what pleases your partner. this takes communication ...before.... any sexual activity. this is the only way you will know what is pleasing and how to as you say "go down" on your girl. not everyone likes the same things.

example i could read every book out there on oral sex with a woman but that doesnt mean my wife will enjoy it. or that I will enjoy it with my wife. what counted is that we during non sexual time together discussed things in all areas of our lives, not just sexual. i knew before anything sexual happened that my wife likes the color orange, likes strawberries, hates being rushed... and much more. so when it came to having intimate time with her I made sure it was enjoyable by having soft cotton sheets, a bowl of strawberries, and we took our time in the forplay, as we went along she would tell me what she enjoyed or how she wanted me to do what, and I did the same. it got quite funny at one point because what she and I enjoyed you couldnt find online or in books. we just did things our own way in our own time.

please dont worry so much about doing it right. there is no right or wrong way. there is only what feels right for you and her. take time to talk with your girl and things will work out in what ever is best for the two of you.