Everyone has something about their personality that makes them unique, and sometimes these traits are more subtle than others. When designing your character and considering how to role-play them, it would be worthwhile to plan what personality traits you would like to portray.
Keep in mind, playing a character with a personality identical to yourself is easy to portray, but makes your characters one-dimensional if they all behave in the exact same way. Rather than making your characters little more than a series of costume changes, try to amplify a particular trait of your own, or to even try to portray your polar opposite.
While you’re at it, you can change more than just a costume and a few traits between characters–try to change your hairstyle, speaking voice, and even your accent if you can manage it. Every little bit helps bring characters to life and make the world a bit more immersive.