If the reason your child isn't ready for lessons yet is because they don't have the finger strength or fine motor skills, try coming up with reasons for them to isolate their fingers as they play. Maybe they have to press a button with their pinky finger? Maybe they need to copy the hand shape you're making? Or what if they trace a picture with a finger that's not their pointer finger?
You may also want to work on gripping. Again, finding reasons for them to practice during natural play will be the easiest way to make this happen. Small colorful pom poms are fun to arrange and to place in small bowls. As they improve, see if they can pick up small pieces of tissue paper? For added fun, let them be the ones to rip the paper up!
You can also help by singing nursey rhymes or playing clapping games. Play music around the house and sing or dance along. Encourage them to move to the beat or to sing along too.
If your child is very young, remember that they will naturally improve as they age and learn through play. Simply by being a child they will get longer attention spans and better hand-eye coordination. But if they are significantly behind their peers, bring it up with your doctor or other professional.