Go over your product, website or story and think about your target demographic and audience. Think about what kind of mascot will appeal to your target group.
Decide how involved you want this mascot to be. You need to know if your character will play a part in a story, feature a distinct personality, or just act as simple decoration.
Write down the idea that your mascot will embody. This will connect our mascot with your own story or product. For instance if you are creating a mascot for a pizza delivery store, your mascot might want to embody "speediness." The idea will also affect the personality the mascot may have.
Begin sketching your character. Create various alternative versions and go over what you like about each one. Consider swapping various parts of one version with another. Keep sketching until you find one that you think will embody the idea that you want while appealing to your target audience.
Draw your character. Take care with your choice of colors, since different colors tell our subconscious mind different things. For instance, the color green makes you less hungry, so making a mascot of a food chain green would be a bad idea. Come up with alternative color designs until you find one that fits.