I have been hobbying pretty regularly for about 36 years now, starting back in the mid '70's when condom use was pretty half hearted although I got real careful in the early '80's as friends of mine (not hobbyists, by the way) started to fall prey to HIV.
Throughout this whole time I have been with nearly two hundred women. The only STD's I got (lice, NSU and the clap) were from civie dating.
No arrests, no muggings, no getting my wallet stolen.
Three NCNS's and one that just said: "So where would you like me to escort you to?"
Not bad considering.
Boldly go!
Here are a few tips to make things safer for you, in no particular order.
1. BYOC if you feel better doing so, but do not be alarmed if the lady declines to use them. I myself prefer to use only one brand of condom because I discovered that using a variety of them caused me to experience irritation. Also, some providers prefer to use their own because they know the packaging is intact, and that the condom is not one that has been floating around in a wallet for the last year or so - not that the ones you brought have been, but this way she knows for certain.
2. Some activities that you may not have thought about that may be problematic. If you enjoy penetrating with your fingers, be sure that your hands are clean, and your nails trimmed. Fingers are one of the most bacteria laden areas of your body, and if you are not careful, can result in yeast infections or vaginitis (non-specific bacterial infection) for the lady.
3. Don't brush your teeth immediately before seeing your paramour. You should most certainly brush your teeth that day, but make sure you brush them at least an hour before you see her. A breath mint is sufficient for fresh breath. Brushing causes micro tears in your gums, and although extremely unlikely, can present a possible source of body fluid exchange. These tiny tears generally seal over within an hour, so as long as you have put adequate time between brush and a smooch, you are fine.
4. If you enjoy DATY but are concerned about possible infection, you might consider a dental dam - a small piece of latex that acts as a barrier to prevent body fluid transmission. With lots of lube, and using your tongue firmly, DATY with a barrier can still be very enjoyable for her. Some feel that the barrier takes away half the fun of DATY (taste) but its a personal choice, and if it makes you feel more comfortable, then go for it.
5. If you feel more comfortable with a CBJ rather than BBBJ, don't be shy about asking the lady to cover you up. She won't be offended.
What it really comes down to is, what level of risk are you comfortable with? There is no such thing of course, as completely eliminating risk, but the use of barriers for all activities dramatically reduces your risk. Opting for DATY without a barrier, or BBBJ increases your risks, but even then, the risk is relatively low.
Good luck, and do try to have some fun too, that is what it is all about!