I think I'll just list some common concept used to make title... (since we're talking about title, I will talk all kind of title, not only manga, since I believe that manga title and other medium title is more or less the same).
- The easiest is just use the protagonist name is the title. Ex: Naruto, Blue Submarine no.6 (name of the submarine), Doraemon. Kagetora, Superman, Batman, Flash, Captain America, etc etc...
- You could even further add a "subtitle" to the name. Ex: Jiguko Sensei Nube (Nube is the name, Jigoku Sensei means Teacher from Hell), Asuka Hybrid (Asuka is the protagonist while hybrid since she was a he... you know what I mean ^_^), Rurouni Kenshin, Mirai Nikki (Nikki is the protagonist, Mirai/Tomorrow is because he could "predict" the future), Tekken Chin-mi, Yu-Gi-Oh (The name is Yugi, Oh/Ou is King).
- You also could use "title" or "job" of the protagonist as the title. Ex: Nurarihyon no Mago, Phoenix Wright : Ace Attorney, Needless (title given to people who have the "power"), Defense Devil (a manga about devil who become a defense lawyer), Ex-Driver (title given to driver who use vehicle to catch bad guys).
- You could also use name of skill that used by the protagonist, or commonly used by people at the manga. Ex: Freezing, Cross-over, Ghost Trick, Zero-In (the name of unique martial art that exist in that manga).
- Or you could even resort to use term that commonly associated with manga that you make. Ex: Shoot (soccer manga), Break-Shot (billiard manga), Dribble (another soccer manga), Katana (though this is about blacksmith manga, not a samurai manga), Vagabond (a travelling/ronin samurai). Some more vague example: You Are Under Arrest (reminds you of what cop usually say), Bamboo Blade (reminds you of Kendo)
- If your manga have some kind of "gimmick" or especially unique thing (could be anything unique, from unique name, location, term, anything...) in it, you could use it. Ex: Apple Seed, Angelic Layer, ZOIDS, One Piece (the greatest treasure in the manga that everyone want to get a hold of), Deadman Wonderland ("one-in-the-world" prison in said manga).
- You could even simply said what is your manga all about. Ex: Mafia, Supernatural, Heroes, Ninja, Shinobi.