@Izzez28 The first step I always take is character personalities and appearances. Um... let's take my friend Anthony. I already know what he looks and acts like.He's the only one of my friends who likes Unova, so I made him grow up there. He's interested in medicine, so I made him a son of Nurse Joy (but he hates that he's the only guy in an all female Joy house). He loves Snivy, so he starts out with Snivy and then picking the rest of his team was pretty easy since he starts in Unova and I know what Pokemon he likes.
That's just my example. Start off small. Baby steps. Characters come first.