You can start by google searching for the type of ghost you want to draw, sketch out some practices, or just set to drawing some ectoplasmic friends right on the glass. If you mess up, just erase with a tissue soaked in rubbing alcohol! It cleans away completely so you can try as many times as you please.
Grab a few candles and make a whole ghost squad if you’d like. Base them on your friends and family, give them names, do whatever you’d like.
Remember: They’re ghosts so their outlines can be wiggly-jiggly like mine if you can’t draw a straight line to save your life (like me!).
Have fun with it! But be safe if you light them and don’t ever leave candles burning unattended.