To answer your question, how does everyone avoids oral STD the answer is world of warcraft especially for most users in this board like sam the hobbit.
Ok now the serious answer, Im one of those guys which picks up girls from the club and not only have oral sex with them but also unprotected one pretty often, in the last year I used the condom only with one girl but I did it cause a friend of mine banged her few weeks before and didnt wanna have any intimate contact.
They are right when they tell you that you are taking risks but in your life you have to make choices, you either play it safe and you take risks and trust me the biggest rewards come with big risks but its up to you.
As a good rule try to keep the lights on when you start so you can see how it looks like, avoid girls which dont shave since you cant clearly see the state, also avoid bad smell which can be a signs of something wrong.
If you have the change to have a shower togheter do it, or have a shower before yourself and hopefully they will get the hint.
Usually good looking girls tend to go with wealthy sporty high class guys which are less likely to have diseases themselves, avoid the club slvt which usually goes with whoever the alchool make attractive to her.