In Book Two, chapter 2, Winston and Julia rendezvous outside of the city in the countryside for the first time. Winston is initially worried about how Julia will perceive him in the bright outdoors and even asks her if she can bear to look at him. Julia responds positively and tells Winston that she couldn't care less about his varicose veins or five false teeth.
When Julia asks Winston what his initial thoughts of her were before she handed him the note, Winston candidly admits that he hated her and wanted to rape her. Julia then proceeds to tell Winston about her personality and background. Winston then asks Julia what attracted her to him, given their age difference, and Julia says,
"It was something in your face. I thought I’d take a chance. I’m good at spotting people who don’t belong. As soon as I saw you I knew you were against THEM." (154)
Essentially, Julia was attracted to Winston's "unorthodox" appearance and knew immediately that he was someone who was against Big Brother.