On yesterday post, I've told you how to add favicon to blogger. But how to make your own favicon? You can search on google but I use the favicon generator from Dynamic Drive. Click here if you want to use their tools.
What you need is an image with not more than 150 Kb size in gif, jpg, png or bmp format. Click browse, choose your image on your computer and click 'Create Icon'. After that, you can download your favicon to your computer and put it on your blog.