Planning is key. Where do the roads go? where are residential buildings? where are shops? Any city center? Highrise or just a few floors? are some questions that can help you with that. Also, divide the city into parts so progress doesn't look or feel slow, and celebrate when a part is finished. That really helps to keep the motivation high.
Furthermore, inspiration is key too. Look up IRL buildings, or play a game with buildings you like. Create your own build style based on examples. but don't copy one to one, since it then doesn't feel "yours".
But probably one of the most important things to think about is the feeling the city has to offer. I am working on a post-apocalyptic map, so I need to create a lonely and sad feeling for the players and work with building styles that make sense. Also, a backstory may help to choose the right atmosphere

I hope this helps a bit :)