Why don't you start with a dinner table and chair set? Find an image of a real table set, and try to build out the shape as best you can. Start with something a bit simpler, just to get familiar with move, rotate and scale tools. If you feel like you're comfortable with these tools, move onto playing around with adjusting vertices and adding new edge loops, so you can move those new vertices around. When you have a basic model you kinda like, try your hand at UV unwrapping and texturing. Once you're done, then do it again, and again  You will begin to see patterns and easier methods to build unique shapes.

     Once you really get comfortable with manipulating vertices, then you could dabble in building a character from reference, if only to see what kind of artist you want to be. Character and environment artists work a little bit differently, both wanting to create high-quality products, but may have to worry about different aspects of how their model is going to be used. In any case, your goal should be to model and texture things to completion. By having something completed, you will have something to compare your future models to in order to improve your skill. By doing this over and over again, you will discover new tricks to use on future models.

     For other things you can try to model: a couple apartment buildings, a couple vehicles, street lamps, city street, and then you can use these things to set up your own city block to render.