It would be pretty boring if all we ever did was drive straight ahead. That's why the turn was invented.

Left Turns

When preparing to turn left, begin signaling when you're about 100 feet away. Less waving your arms frantically out the window, and more using your left turn signal. There you go.

Now move over into the left turn lane or, if there isn't one, a teensy bit closer to the center line. Slow down (doi) so that you're able to bring your vehicle to a stop just before reaching the limit line, if there is one. 

Check the traffic to both the left and right before making your turn at an intersection, and make sure you turn widely enough that you're not cutting into the corner of the lane of opposing traffic, but not so widely that you take out a few telephone poles and a mailbox. It's a delicate balance.

Remember that the only time you can turn left when you have a red light is when you're turning from a one-way street onto another one-way street, such as on your Spring Break trip to downtown Stockholm. If you're in that situation, signal and stop as you would when making any left turn, and as long as you don't see any signs prohibiting it and there's no one else with a green light approaching the intersection, you may proceed. 

If you do have to yield to other traffic, the worst-case scenario is that you may have to wait a minute or so for your light to turn green. Oh, horror of horrors.

Right Turns

As with the left turn, signal 100 feet before reaching the corner, slow down, and drive a bit closer to the right side of the road. Make sure you aren't blocking any cyclists or a bike lane. If you do have to wait to let a bicyclist pass, try to keep the obscenities to a minimum. And keep 'em to yourself.

When you arrive at the corner, make your right turn as soon as you have looked both ways and have determined that it's safe to do so. Turn into your lane. In other words, don't make an overly wide turn into a far lane, even if you'll eventually need to be there. You'll have a chance to get over later, we swear. Besides, how cool is it that you have your own lane? Might as well make use of it.

If you have a red light, you may still go ahead and make your turn, as long as you don't see one of these bad boys:

 

(Source)

If there isn't a "No Turn On Red" sign, proceed cautiously and always yield to anyone with a green light or a "Walk" signal, then go ahead and make your right. If you have a red arrow, the same rules apply as a red light when turning right. 

Examples

Turns are so easy, a child could master 'em. To demonstrate this point, below are examples of left and right turns, as diagrammed by a 6-year-old.

Left Turn from a Two-Way Street

As you can see in the diagram above, the artist's "Mommy" is (barely) in the left-hand lane and is turning left. She may turn into either lane of the cross street, including the one nearest the...dog?

Right Turn

In the same diagram, the polka-dotted car is in the right lane and is turning into the rightmost lane of the cross street, rather than making a wide turn into the other lane. Good job, polka-dotted car.

Left Turn from a Two-Way Street Onto a One-Way Street

In the diagram above, there's an ice cream truck (See the ice cream cone?) about to turn left onto a one-way street. It may turn into any open lane, thankfully taking the ice cream out of the reach of the jerk at right, with whom the artist apparently has some bad feelings. 

Left Turn from a One-Way Street Onto a Two-Way Street

The artist's school bus, currently traveling along a one-way street, is preparing to turn left into two-way traffic. The bus may also turn into either open lane, as long as it's safe to do so. Hopefully the driver can make the turn while ignoring all distractions inside the vehicle, like Timmy's impromptu farting of the alphabet.

Left Turn from a One-Way Street Onto a One-Way Street

In this example, the taco truck can turn from the far left lane into any safe and open lane to the left. Perhaps the taco truck driver will be fortunate enough to happen across the artist's left shoe, which has been missing since Thursday.

Right Turn from a One-Way Street Onto a One-Way Street

Note Billy's mom in the same illustration—she's in the far right lane and turning right. She has her pick of any open lane. If signs are posted that allow it, she may even be able to turn right from a different lane than the one on the far right.

Turn at a "T" Intersection from a One-Way Street Onto a Two-Way Street

In the picture at left, there is a rather pointy car turning left from the center lane of a one-way street. In this example, vehicles in the far left lane may be turning into the near left lane, and vehicles in the far right lane may be turning into the nearest right lane, so the car in the middle lane should always turn into the lane that's furthest away, whatever direction it's going. 

It better get a move on, too, because it looks like that masked bank rob[b]er is up to no good.