You dont have muscles in your fingers to train, silly
The fingers are moved partly by muscles in the hand, but most of the work is done by muscles in the forearm. These muscles do not attach directly to the different joints of the fingers, they attach by means of long tendons.
I could suggest rock climbing as a way to ensure that you are stengthening the areas in which helps you have a better "fishhook of death"
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*Edit: Also, make sure that you concentrate on having good form on your grip while doing your other weighted exercises. This will help in the area in which you want to improve as well.