Black pines are trees that can be very rewarding. Unfortunately as bonsai trees, they require patience as developing branch structure takes time for growing seasons to pass.
To develop ramifications on your black pine bonsai tree you often have to deal with leggy growth. Don't be discouraged by this as even a leggy branch can be turned into a full looking pad layer. In order to do this, you'll need to train your branches to come back toward the empty sections of your branch. This will require you to continually keep up on candle cutting and bud selection each season.
Plan your candle cutting to grow back towards the inside of the primary branch. The secondary branches over time will reach the inner portion of your primary branch and fill in the entire pad. If you are fortunate enough, inner branches will develop as well giving you further options on developing your pad layer.
Above is a simple birds eye view explanation showing how to develop your branches over time to fill in the layer. Each season we save two pairs to from each secondary to develop. As we save two pairs each season, the branches will have exponential growth and at some point you will need to start eliminating branches.