Ramza's Yell is the move that can raise speed on other characters, though his Scream raises Brave, Attack Power, Magic Attack Power, and Speed, but only for himself, which can make him an effective Thief.

I generally bring my party's Brave up to 97 with Ramza's Scream as soon as possible. I had Mustadio learn Preach and raised everyone's faith up to 79, (It annoys me when they complain) and Ramza's to 97. It's a good team.