Kearney's book on tracking is good. The early Tom Brown books were good as well. There are many books out there, and most have the same basic skills.

You have to ask yourself first: "What will I use tracking for?"

Many of the books and schools are geared toward either military tactical tracking or fugitive recovery. The basic skills are the same, it more about how you organize and operate.

The key to learning initially is to learn to be more observant in whatever environment you are in. When tracking, you are looking for sign that is out of the ordinary, different, that doesn't fit. You also need to observe more about how people walk, types of shoes, and other human behavior.

Learning observation techniques is also important, for when you are searching for sign. You must observe in an organized manner, and observe comprehensively. An old friend of mine runs a very good school: ASF Combat Tracking

It is geared to military and law enforcement though. There are others.

Yes, I have had quite a bit of training in tracking; several SERE schools, sniper school, strategic reconnaissance school, and others. Most of my training was focused on evading a tracking team or dogs though.