You're 17, so you've probably got the STD talk at school; you know that bullshit where they tell you to go for abstinence and don't tell you a fucking thing about not getting an infection, so here's some tips:
1. Wear a condom, put it on properly, roll it down the shaft, and pull the tip out
2. Genital herpes can not infect your mouth, or any non-genital part of your body, so as long as she hasn't got warts or HIV, get your face in the kooch. You might get some sores, but it won't be a lasting infection.
3. Genital herpes can still infect your genitals, if contaminated parts of your body touch your genitals. If she touches herself, don't let her touch your dick until she's washed her hands, THOROUGHLY like pre-op surgery thorough. Also, go all at that kooch, but wash your hands the same before you touch your dick. You might want to get some of that hand cleanser stuff so you don't have to make a run for the bathroom.
That's pretty much all you need to know, other STDS can be cured with an injection, so don't worry bout those ones.
EDIT: If you eat her out don't spit on your dick to lube. Just keep track of any part of your body touching hers, and know how and where you can get different infections.
EDIT2: Sex with older women is fantastic, don't have sex with any of your 17 year old lady friends, you might be their first, and you don't want to ever be a woman's first, because you will, and I repeat that, YOU WILL, break her heart, and if you have a conscience then you don't want to have sex with that girl and end up feeling guilty forever about how the relationship ended.
Also, so women enjoy giving oral sex, you can tell who they are by whether it felt good or not, so if it felt good, don't look into it to much, if it was a shit blowjob, be cautious.