Children need as much practice with fine motor control and the pencil grip as they can get so I'd have them do a mix of play using their fingers, a mix of different activities involving the use of their hands, drawing activities and tracing lines. (For older children, I have them trace stencil sheets.)
There are many line tracing worksheets on the internet, some free while others are paid for. I have many books that I use bu they don't always contain the things that I want children to practice. With that in mind, I've made my own tracing book and I am sharing this with you, my dear readers, for free.