This is our first dog for blood tracking, so I am not an expert on the subject either. As most guys said, get John's book, it is a great resource. Look at their information on the web (borntotrack.com). If you look at Jolanta's blog she put up a post about our pup (a smooth haired dachshund) around the 1st week of Jan.
The big thing we learned very quickly was to progress the tracks as your dog progresses and don't let him get bored. We started by dragging a piece of deer meat (like the size of a tennis ball) on a string, wetting it occasionally with the diluted blood that comes off of thawing meat, and aging the track only a couple hours. This was great for him at 8-9 weeks, but he quickly got bored with these tracks. We progressed to dripping diluted blood (like 2-3 tablespoons of raw deer blood diluted to a quart with water) and making longer, more difficult tracks. By 12 weeks old he was doing tracks 300-400 yards long, with several 90 degree turns, that had been aged up to 12 h. Since about 15 weeks of age our tracks have gotten much more advanced. There is NO WAY we can use raw deer blood with Oskar without diluting it, because at this stage of his development he'll wind it at 50-100 yards ahead and try to cut the corner to get to it (like Bowmania said about carcass winding). This is OK for finding deer, but for training I want him to stay close to the line at this time, I'm sure he will mature out of this phase.
Oskar found his first deer at 12 weeks old, and found 12 deer this season (all by the time he was 5 months old). 2 of these tracks were 500 and 800 yards long. If your dog has the focus and drive you'll be surprised with his progress. Any dog has the nose (and more) to do it, that part is easy, it takes the focus and ability to concentrate, and a handler that can read what the dog is doing to make it work.
I think the hardest thing for many owners is getting the dog on enough real tracks. We made a dedicated effort to get Oskar on 10 recoveries his first year. I want him to average at least 15 recoveries a year going forward. This takes alot of work and dedication, but I don't know how a dog that tracks 2-3 deer a year can ever reach his full potential.
Ryan