Being predictable means doing what drivers expect you to do, and not surprising them. It doesn't mean that drivers will have to think and analyze in order to predict your behavior, it means that they automatically know what you are going to do without thinking a lot. Predictability comes from following the rules and using hand signals, but also from using proper lane positioning. 

Being predictable means:

•  Ride on the right

•  Obey all signs and signals

•  Don’t turn left from the right side of the road

•  Don’t swerve or turn suddenly

These are pretty easy things to do, but it is common to see bicyclists violating each of these rules, sometimes more than one at a time. I emphasize over and over that you must look and verify that it is clear before moving to the left. We practice looking over the left shoulder without swerving, one of the most important basic skills for a bicyclist.

Turning left can be a challenge, especially for kids. On large streets with multiple lanes and heavy traffic, left turns can be challenging even for the most experienced cyclists. I teach the Box Turn, or Pedestrian-Style Left Turn for those situations.

To make the box turn, approach the intersection in the lane position appropriate for going straight, and do not make any hand signals. As you cross the intersection, angle slightly to the right. At the other side, stop and turn your bike. Don't swerve to the right and then go straight across, because a following car may see the initial swerve and think you are turning right. The reason for angling to the right is so that your bike will not be sticking out into the lane after you stop and turn it. You want to turn your bike and then be in the proper position to go straight across the intersection again. You must wait and re-negotiate your turn with any other drivers or bicyclists, then proceed. If done properly, this can be easy and safe, but if done improperly  can be dangerous. The most common mistake is not stopping and re-negotiating before doing the second crossing. This effectively makes it a left turn from the right side of the road, which is #2 on the list of bicyclist mistakes that cause crashes (see the table)!

I call lane position the traffic equivalent of body language, because it tells drivers your intention without the use of explicit words or hand signals. They will generally understand it subconsciously, just like with personal body language. It is also important not to send mixed signals, with your lane position saying one thing and your hand signals saying another. This is common with kids, whose control over their lane position is not always very precise. Proper lane position when approaching an intersection on a two-lane residential street is 1) far right for turning right, 2) left side of the lane for turning left, 3) far enough from the right edge of the road that drivers will know you are going straight and will not give you a "right hook" if you are going straight.

Of course if there are special lanes like right-turn only lanes or left-turn only lanes, you should use those for turns and avoid them if you are going straight.

Here are figures from the California Dept. of Motor Vehicles Driver Handbook, which most drivers use as a study guide when applying for or renewing a driver's license. These show proper lane position for various maneuvers, and also a Box Turn.