As someone that did a lot (ie. thousands and thousands) of cold walk-ins in sales there are a few simple principles to follow that aren't specific to aviation but rather relate to selling...after all, you are selling YOURSELF.
1. SMILE. Even if you don't feel like smiling. If you walk in there frowning or looking beat (and let's be honest it won't be fun getting out there to hand out resume after resume). Smiling, not grimacing, makes you look friendlier, enthusiastic, and more approachable.
2. DON'T JUST STAND THERE IN SILENCE. Acknowledge everyone, doesn't matter if they are the Chief Pilot or CFI or the receptionist. Remember that even people 'lower down the chain' can be the person that advocates for YOU and gets YOU hired, and likewise they can just slide your resume in the bin if you rub them up the wrong way. So start out with a friendly 'Hi!' as soon as you walk in, ask how they are going (and listen to the answer). If they are really busy ask if you can come back at a quieter time and what that might be so you don't annoy them by lingering.
3. KNOW YOUR TARGET. You are walking in cold, but that doesn't mean you shouldn't have done your research first. Check out the organisation online. Know their fleet. Know their staff. Do you know anyone that works there? ...and so on. If you are well prepared it will give you conversational material to make small talk and impress anyone that you speak to e.g. "I read online that you have just signed a contract with a Chinese airline for training, that sounds exciting!"
4. A FIRM HANDSHAKE IS KEY. Practice this. Don't do the 'death grip'. Don't EVER do the 'wet fish'. Doesn't matter if they are female or male, you offer your hand and say your full name, not just your first name. If they don't say their name, usually "I didn't catch your name?" works. This is important so if you are following up with a phone call later on you can mention who exactly you spoke to.
5. BE PRESENTABLE and the SORT OF PERSON YOU WOULD WANT FLYING YOUR AIRCRAFT. Neat hair, nothing crazy long or weird styling. Clean shaven. Make sure, for the love of God, you are wearing neat clothes (ie. collared shirt tucked in and decent shoes). If you have no fashion sense get a suitably qualified friend to give you some advice.
Hope that helps, and good luck!