Generally, it's spread through sharing saliva (kissing, sharing food or utensils, sneezing on somebody, etc.) When you get diagnosed with mono, they tell you not to kiss anybody and not to share drinks or utensils, but they tell you that it's okay to go about your daily business otherwise. Studies have shown that people who are living with people who have mono really aren't at an increased risk of getting it over the general population (their risk maybe increases 1-3% or something... I don't remember, but it was small).
So wash your hands, make sure that your friend isn't licking things, don't share a drink or water bottle, don't share food... And you should be okay.