The most common mistake people make during oral sex is not using protection while doing it. For safer oral sex, use a condom to cover the penis. Dental dams can be used to cover the vulva, vagina or anus.
Another common mistake is having multiple sexual partners as more people means more chances that someone may be having an STI.
It is also important to be aware whether or not your partner is infected before having oral sex with them. Do not hesitate in asking them to get tested.