So is there a consensus as to how to get manageable traffic? (ie, roads not full congested during the day)?
1. Use the capacity of avenues as throughfares for large volumes of traffic to pass through. Don't zone directly on the avenue as it causes traffic. Branch out side streets from the avenue using medium density roads (to avoid traffic lights), and then zone on those side streets. If the side street has no outlet, be aware that this could cause traffic by hordes of cars entering the street looking for something, and then having to make a U turn at the end when they can't find it.
2. Be aware of the right of way properties of intersecting street types. You want paths of travel that have the highest volume to have the right of way as much as possible. That way, they don't have to stop for other cars. For example, an avenue with a medium density or lower side street stuck on it will have the right of way. Cars traveling on the avenue can be free to go without having to stop for other cars. Another example is a high density street with a medium density or lower street stuck on it will have the right of way, too.
3. Minimize traffic lights. They are inefficient and usually hold up traffic more than help it. There are some cases where traffic lights can help congestion, like in a tight area where lots of cars want to turn, but those cases are rare. Most of the time, you don't want any traffic lights.
4. You will inevitably have traffic lights when you have a 3 way or 4 way avenue intersection. Try to keep these to a minimal. Try to avoid 4 way intersections, and keep all your avenue intersections as T intersections.
5. Try to visualize the path the sims will take according to their desire to take the shortest path possible. When sims travel long distances from one place to another, you want to make sure that avenues comprise the majority of that shortest path.
6. Keep in mind the sims' destinations. There is morning and evening rush hour traffic, so sims will be going to work. University is at various times throughout the day, and shopping is whenever the sims feel like it. To ease shopping congestion, zone commercial mixed up with your residential, so that the sims can walk to shop. To ease the conflict between workers and students, place your industrial/factories in a spot that will not cause students to take the same paths as workers.