Suffice it to say here that the handler may not do anything to assist the dog in determining the direction of the track. Sometimes handlers follow closer than the required 20 feet behind the dog when he is tracking, but not often. You probably know that the rules now require a visible marker to be on the lead at the 20 foot mark. If your dog gets tangled in his lead, you may drop the lead, walk up to the dog and untangle him. Then, it is a good idea to take a few steps backward, and wait until the dog has proceeded at least 20 feet before following.
Some handlers seem to think there is a rule against talking to the judges on the track.
If you are not sure about something, especially as it relates to a particular judge's interpretation of a rule, then turn around and ask. This is especially useful if you are uncertain about guiding or otherwise helping the dog. In TDX, you might want to clarify from the judges just how far you can help your dog over an obstacle, if there is a question as to whether your action might be considered guiding. Most of this is just common sense and some knowledge of the rules. There are several common errors I see handlers make over and over again.