It's mostly balance, you need the right amount of workspaces for how many houses you have. Most of it is trial and error until it balances out. To lower traffic and pollution use rail systems instead of roads. You can actually build a town with all rails, and no roads. Land values are effected by what type of sims live there, rich, medium, poor etc. If a house is next to a power plant, or other undesirable location it will also lower it's value. Be sure to build your power plants as far away from the city as you can, as they also greatly effect pollution.