have a hand in

1.  Also, take a hand in. Participate, be involved, as in I'd like to have a hand in planning the publicity. [Late 1500s]
2.  have or keep one's hand in. Be actively engaged or remain in practice doing something. For example, He works as stage manager, director, understudy--he has a hand in every aspect, or Write a few pages every day, just to keep your hand in. [Mid-1700s]