Create a template on your illustration or editing software. Decide on the size of your panels. Some prefer panels with the same aspect ratio of a TV set, a movie theater or a shape halfway between the two. Of course, yellow sticky notes work just as well. It's all a question of how you want to do it.
Illustrate your panels. The artwork doesn't have to be perfect.
Put your panels up on a whiteboard, and write the dialogue that happens in that shot and any action that happens. If you are working in a group, this is a good way to get everyone's input. Move the panels around, adding to them until you get the sequence you want.
Scan the pictures into your computer and put them together as a slide show. Record a rough dialogue track yourself. You can make this as "professional" or as rough as you want. You can add sound effects or make the sounds yourself, even add a soundtrack if you're so inclined.
Once the storyboard and rough track is approved, make a shot list from it. List shots you will need from every location and sequence. This will save time when you film. Use the rough track and storyboard as a blueprint when editing.