I have created races for my group's games and RPG settings for near on a decade!
How I created initially was "I want desert humans" so I would plonk down humans on a desert region and give them 'deserty stuff'. Which is alright if that is how you wish to go but these days I base it off evolution and/or magic if they are a magical race.
A species or race borne from the desert will be taller and have flatter noses because it irradiates heat more efficiently. They may have thicker eye lashes and beards to protect them from the windshear and sandstorms.
Deep jungle races would be(at least in my view) a little shorter and wiry from the lack of larger nutritional beasts that you might find in open areas.

typically I settle on geographical situation, resources and wildlife. they usually determine (for me) the customs, temperament and appearances of races.