Well you can't be samurai at first since it's a advanced class. But generally it's best to play as what you want your samurai sub to be at first, I hear warrior or monks are the best subs for them (typically warrior though for provoke and such)

It really also depends on your style on which sub you go with for samurai as most melee tend to work out well with it.

Although you can find out more about samurais at ffvault.ign.com and check out the samurai forums they got there for more detailed stuff and also check out the actual samurai section for info on thier skills.