That is an interesting question. Also pretty involved. How old is your lab?
By wounded game, I take it to mean blood. Like you arrowed a deer and can't find it?
Can you get your dog to put its nose on the ground and acknowledge a scent right now?
Do you have a long lead or check cord?

Quick and dirty. Save some blood from your next deer kill, or the blood that collects in the bag or cooler from boning out an animal. Or ask your local slaugher house for a bucket of blood from the next steer they kill.

Freeze it in baggies, it may coagulate, but you can mix with water to lay a track.

Put your dog away so he can't see what you are doing. Get a cup of blood and a little paint brush. Dip the brush in the blood andfling it on the ground in your yard,every two or three steps. Make a track around your yard. At the end, have a nice pile of meat scraps for the dog to eat.
Bring the dog out and give him a signal. I say "sick sick sick sick" really fast, it is to simulate the sniffing sound a dog makeswhen tracking something. My dogs know this means to turn it on and track what I point to on the ground. This track will be like a lighted runway to the meat. He will think, this is fun, lets go again. This is done ON LEAD, so you can pull the dog back on later when it gets difficult.

You do this every other day, set the dog up to succeed so he really wants to do this. Make a ritual of some sort of making him see you are getting the "tracking stuff" out, he/she will know what its job is going to be.

Over time, make the tracks more difficult, longer tracks,use a smaller brush, smaller amounts of splatter, farther apart, more diluted, longer timeout before starting the dog. Get to where you get down to half blood half water, on a 1 inch by 1 inch sponge, dabbed on the ground every two or three PACES, ormore. There are dogs that are very good at this, they concentrate very well. Some have done tracks 1000 meters long and 40 hours old layed in this fashion.

On longer tracks, have areas where the animal layed down, a bed with a pool of blood, and some meat scraps as a treat to keep them interested along the way. Also when you go to the woods to lay a track, put cotton balls up in the trees to mark your way, you will not be able to see the blood. This will aid in helping you know when the dog has gotten off the track.

Just a place to start.