Write a set of instructions for something you know how to do by heart. This could be a recipe (your grandmother's brownies), an emotional process (how to fall in love), an act of craftsmanship (how to weave a basket), or an action so simple you may not remember how you learned it (how to tie your shoes). Be specific in the details that you use, and allow the instructive voice to become formal, colloquial, or intimate as appropriate. To whom are you giving these instructions? Why is it important that this information be passed on? Trust in your deep knowledge of the subject you're writing about, and let the language that describes it surprise you.