As discussed in Shogi Strategy, an optimum attack force will consist of Rook, Bishop, Silver and Knight. A pawn or two at hand will also help. Please see the demo play below. In this Yagura game, Sente was able to formulate an attack force while protecting his King with safe Yagura castle. You can either click '>' button to see how the attack is initiated. (some branches show alternate moves by Gote), or you can click '>>' button for the automatic replay.
You may rewind ("|<" button) the game and play it from the beginning to see how this formation is built. If your opponent is a good player, he will try not to let you build up your attack like this, before the actual attack starts. That's what the excitment of Joban and Komagumi is all about.