I made a sewing pattern for a bike helmet cover, but this technique can be used to make a pattern for just about any object, even people!
Step 1: Cover and wrap the object
Step 2: Make some guide marks
I marked the ventilation holes on the helmet and the stripe I will eventually put down the centre. I also marked along the bottom edge of the helmet.
Step 3: Cut it free
Step 4: Cut the pattern pieces
Draw the lines first with a marker and make extra marks to show where the pieces match. If you don't do this, you could end up with a bunch of weird shapes, not knowing how to put them back together!
Don't forget that you can also cut "darts" to make a pattern piece flat without cutting it in two.