Hello,
My suggestion, if you are wanting to do some tracking/trailing for fun, and you have a food motivated dog, is to look into spray tracks.
I've seen several SAR K9's started with this method and went to a seminar where a PD K9 trainer used it and was very impressed with the theory behind it and how it worked.
It starts you on a hard surface then moves to other surfaces...think of it like teaching your dog to smell for carrots, (scent on pavement) then moving to the 'stew' of many scents (grass surface where you have scent, disturbed dirt and crushed vegetation) but your dog has already learned to smell for carrots, so they only look for those in the stew and don't get lost, or overwhelmed. Not to mention, do NOT become a vegetation tracker.
It also teaches nose down behavior as the beginning step, instead of letting the dog try to figure it out. It also does not rely on prey drive (or the tendancy to chase) to get the idea through their head.
You can go here for a synopsis of the methodology. I also have it written up in draft form.
http://uspcak9.com/training/scent.shtml
You don't have to use a sweaty t-shirt, just use water that doesn't have chlorine in it.
You can also teach down on article and incorporate it. Useful for when you loose your keys in the yard.