Step 1: Figure Out How It Was Made the First Time.
Once you have that squared away you can make the pattern, I usually use newspaper because it's free and is similar enough to pattern paper that it works pretty well. In some of the pictures, however I used regular lined paper because it shows up better in the pictures. Measure the pieces, this is easier if you have a sewing tape measure but it can be done without; I lost mine when we moved so I made one out of some scrap cloth marked at 1/4 inch increments. Take your time with it and double check yourself and be sure to start right at the seam and follow it as closely as possible, making note of any curves.
Keep in mind though that this method produces a pattern that is roughly a 1/4 to 1/2 inch smaller than what you are measuring off of because you aren't able to include anything beyond the stitch. To compensate, simply make the pattern 1/4 inch bigger all the way around by marking 1/4 inch bigger all the way around(see picture 7), I usually do tick marks and then go back and connect them because it seems to go faster. I made this for my daughter however, so I left it as is to make it smaller, and you can likewise adjust your pattern to be bigger or smaller as you like simply by adding to or removing from the pattern (see picture 8). In general, sizes go up or down by 1/4 inch for babies, 1/2 inch for children, and 1 inch for adults but somethings won't follow that rule- hats for example since your head grows less throughout your life than the rest of you. For this reason is never a bad idea to take a few measurements from whoever will be wearing the clothing (head circumference, shoulder width, waist size, etc) just to be sure.
And with sewing is best to err on the side of being too big instead of too small since you can always take it in but you can't always add to it.
Step 2: Sew It Up
Before you begin sewing double check your measurements while it is still just pined together and easy to adjust.
Once you are satisfied, sew it together. Since the hat I was copying had an inner lining, I first sewed the inside and outside separately and then turned them inside out and sewed them together and sewed the hole closed after flipping it right side out. At first I wasn't sure how the ears were attached but looking closer I found that they were simply sewn onto the outside (something you can get away with when working with fuzzy material). I also decided to change the ears a little bit; be sure to decide what changes you want to make before you start sewing to avoid having to pick out stitches later :)