It would be a romantic thing to claim that John saw any sparks flying between them or felt something like electricity during the first physical contact with Sherlock. Or a ridiculous thing. They say such things in certain novels, right? Well, HIS life was most certainly not a novel, thank you very much!
Anyway - nope. No such things, no sparks. John was standing outside 221B, waiting for his potential new flatmate, and the potential flatmate had just exited a taxi and greeted him with a "hello!"... which was at least more cordial than during their first encounter, because then it had taken John lending him his cell phone before that strange man had even condescended enough to acknowledge his presence.
Maybe Sherlock Holmes had made up his mind as to remedy a bit of that first impression (for the obscurest of reasons, because he hardly ever seemed to care). But maybe he had - so, when John had answered with a rather formal "Mr Holmes", he corrected him. "Sherlock, please." It was the inflection, the melody in the last word that caught John's attention. One could have mistaken it for mild annoyance about wasting time with formalities, but it was more something along the lines of "Hey, I actually can do MUCH better than back in the lab if I want to!" Simultaneously Sherlock extended his gloved hand, they shook hands briefly, and that was that. The first touch. Yeah. Spectacular, right!
Or was it? John recalled a touch of soft leather and a firm grip - not too obviously domineering, and strangely reassuring. He was not Sherlock "Ishakeyourhandanddeduceeverythingaboutyou" Holmes, so that's all he got from that. Not much, but good enough for him. And then Mrs Hudson showed up, and Sherlock actually hugged her, put his hands and arms around her, and that was much more affection than John would have given him credit for. Interesting.