I have been to several conventions from Comic Con (the biggest I've attended) and WTF Con (Smallest I've been too). KomicKazi, Anime Con, and Wondercon as well.
Conventions may see seriously overwhelming at first because of the crowds but they are a lot of fun. The first thing you will want to do is go to the website and examine all the panels and special guests that they have listed. Once you figure out what things/people you want to see, make a list of the times and where they are at. you get these helpful booklets when you register that have maps and where the panels/autographs are. Just take your time and plan things out.
As for the people; A majority of them are the nicest people you'll meet. I have talked to several dozens of fans while waiting in line for autographs. We talk movies, games; whatever and just have a good laugh.
However there are those who are iffy. I've seen some idiots act like a bunch of jackarses. They are very grabby for swag and are not afraid to push themselves past you to get free swag. Some are just the sterotypical basement geeks who don't understand what deoderant is.
But again, a majority of them are very awesome. Just remember to keep an eye on your stuff, bring lots of things to keep you entertained during long lines, and carry cash (a majority of autographs are cash only. Shops though tend to accept ATM cards thanks to those nifty credit card dongles for phones).
As for meeting actors/actresses - they generally are very wonderful people. Never feel afraid to talk to them and ask questions that you are curious about. Most celebrities are very friendly and fun to talk too.
Finally when it comes to Cosplayers. If someone is in costume, they generally expect/understand that you'll want to take photos of them. Always ask first but they generally are more than happy to pose for you.
AND HAVE FUN AND TRY TO SMILE BETTER THAN ME (right)
1. I go with friends but on rare occasions, I go by myself. If I go with friends, I make sure they all know that if I see something or have a panel I want to see - I won't wait for them and they should not wait for me. We'll always meet up after the event.
2. I split the hotel fee. You can usually find them for cheap if you book it ahead of time.
3. For splitting a room with someone you just met - it's usually nervous at first since you guys are new to each other. Just make sure you both respect each other's space.
4. Getting badges is a painless process. Some cons let you pick them up early. Most, however, have you wait in a registration line. You give the person your name and if you have an email confirmation ticket, you show them that. They hand you the badge. DO NOT LOSE IT! Always keep it visable on your person.
If anyone ever has questions about cons, I am becoming a con-addict so feel free to ask me anything I'd be more than happy to offer advice, share experiences, what have you to any of you.