I'm a newbie to SC4 myself (though I used to play SC2000). My advice, before you even BEGIN to build a city is play around on a blank map with roads. Learn how different kinds of roads work together, how they look when you try and lay them different ways, etc. I've found that the road structure of a city is one of the most important factors to making it aesthetically pleasing and realistic. So that's my advice: roads.