Writing grows best a little at a time, most days. Before a child writes something down, let them say it out loud first, telling back a story, describing a picture or a walk, until the sentences come easily. Then write a few of those sentences down, and read them back together. Copying a short, good passage, and later writing it from dictation, teaches spelling, punctuation and sentence shape all at once.
Handwriting is a separate skill, and a few minutes a day does more than one long session a week. Sit well, hold the pen lightly, and stop before the hand gets tired. Palmer's drills and the Spencerian copies were made for older children and adults, so a young child may only manage a line or two at first. Some usage and a few rules in these books are old-fashioned; where they differ from what is taught now, go with the modern rule.