Hey, Mario. We'd be glad to help, but I think a little more information is required.
Arms are the part of the body I focus on the most... but you've given no information to work with. Training schedule, type of workout (ie heavy weights/low reps, light weight/high reps), and so on.
Are you an all around hardgainer? Or do you just have a hard time devoloping the arms?
And also, Gorilla has it right on, if you're looking for more basic info.
I superset arms... every workout. It's been the key to growth for me. My arms sucked until I started working them on the same day.