Would one need any thing special to keep in mind? Are there any unspoken protocols that people follow?
I have heard that most VCs won't entertain you unless you come through a referral. Is that true? If so, what can someone without contacts do to at least be able to pitch to them?
A referral is the best way to get a meeting, but it's not the only way. Many have open office hours that are a great time to meet them and get them interested in what you're working on. They attend events (or their Associates do), and if you have a chance to make a good first impression, you can follow-up from there.
In general, they want to find entrepreneurs that are doing noteworthy things, so the best way to get a meeting is just to execute on your startup, and don't be shy about highlighting your successes.
The other thing you should be doing is making contacts. I've always liked what Dharmesh Shah said: "Your probability of success is proportional to the number of people that want you to succeed." You're going to need a ton of help as an entrepreneur and not just with funding. You'll need intros to mentors, potential hires, potential customers, and more. Get out to some events, be friendly, be helpful, ask for help when it makes sense to do so, and build your network.