I carry a small spray bottle with peroxide in it and get down on my knees when blood is hard to find. Sometimes leaves have red spots on them and it's hard to tell by looking at it if it's blood or not, so I spray peroxide on it and in pine needles and such. The peroxide will let you know quickly. If it's blood, it bubbles with peroxide. Niffty trick.
BBO

10-4, Good Buddy!

Practice and patience!

Get a high intensity flashlight with interchangeable lenses. The blue lens really makes the blood stand out. i have located three deer and a huge elk for other hunters using this light.Seven folks had looked for the elk since morning and had given up:Then we found it within 45 minutes with the light. Get some of the biodegradable one inch blaze orange or redtape that surveyors use for marking the blood trail.

Double lung them and you can watch them fall over, and hopefully you can walk 20-60 yards.

Gerber Blood Tracking light works excellent.