Japan's event is really different from North American Conventions. I've been to Hong Kong's ComicWorld before so I do sorta know how Asian cons goes. I did a tons of research before hand to made sure I don't completely embarrass myself LOL This post is going to focus on the basic of going to a Japanese doujin event.
Conventions are called '同人誌即売会' 'doujinshi sokubaikai' or what most people call, 'event'. These event's sellers are mostly fans. Keep this in mind. Unless it's a big event like comiket, you usual don't see stuff like actual manga, games and figurine. There are actual stores to buy anime merchandise. What you will find in a typical event are doujins (fan comic), fan made games, prints, keychains, bookmarks, craft etc.
Some times, there are a few events going on at the same time. For example, the event I just went to is a combination of ComicLive (Selling Soujin), Cos-Day (cosplayer event), and World Cosplay Summit Japan preliminary round. Some times, it can be a few Only Events (events that are focused on one anime/manga) combined into one.
Now, Japan's events have a shit tons of rules for both con-goers and cosplayers. Make sure you read the event's site properly before you go. I'm only going to list some of the important rules.
Depending on the event, there might be an extra charge to cosplay.
You cannot wear your costume to the event, and you cannot leave in it. You must change at the event.
Changing rooms are provided so do not use the washroom to change.
Prop rules differ between different events, each event have a different size they allow, please check the site for more information.
Realistic looking weapons (eg. guns) are not allowed.
Cosplay photography are only allowed in the cosplay-zone.
Music, or any actions that will cause disturbance to the general public are not welcomed.
Highly revealing costumes are not allowed, you will be asked to cover up or leave the event.
The change room from my last event is pretty much just a secure space with nothing in it. No chairs, no mirror, no actual changing space. Everyone sits in group or in front of walls and mind their own business. Make sure you wear something underneath if you don't feel comfortable with changing in front of everyone.
Cosplay namecards are very common over there, if you are planning to talk to some people, go make some cards. (I didn't, and I didn't talk to anyone too so...)
Japanese cosplayers use luggage to carry their stuff around. (It's like a mini work station, it's actually really convenient) If you get lost, just follow the people with luggage! There's also a space where you can store your luggage for a small charge.
For con-goers (planning to take photos)
Depending on the event, there might be an extra charge to photograph
For most events, NO PHOTO OUTSIDE OF COSPLAY ZONE.
Video taking is strictly prohibited.
Digital cameras or cell phone that can take videos are required to register with an photo ID, still you cannot take video. (I got away with not showing my ID for my digital camera last event. but I'll see how it goes with my next event)
Tripod and other photography tools are not allowed (Check the websites for more info, I believe certain lens are not allowed too)
You must ask the cosplayer politely for a photo, they have the right to refuse you.
Don't take photo of people when you don't have permission, or when they are not ready.
Don't take indecent photos. You know what I mean.
One of the ways to ask for a photo is 'お写真いいですか?' 'O sashin ii desu ka?', or they will probably understand if you point at you camera LOL. Afterward, make sure to say thank you or bow your head, even if they are still posing for other people.
I found out about my event through http://www.youyou.co.jp/, it is a company that runs dojin events. There are a few more wedsites like youyou, and Cosplayer Archive also have a list of events going on. If you are planning to go to Japan, check if will be a event going on at that time!
Just use your common sense and manners as to what to do and what not to do. And most importantly, have fun!
Part 2, my actual experience at a Japanese convention is here: ComicLive