First off, before i start tracking anything i evaluate how the animal was hit, I like to wait 10-15 minutes to start tracking in most cases, unless hard rain. If it is dark, you need good light, dont even try tracking using a weak light. When i begin tracking i locate where the animal was standing or running when the shot took place (or as close as i can) i will closely inspect the surrounding area very slowly, being carenot to step anywhere i havent carefully looked over. Sometimes i will find a good amount of blood where the shoot took place, other times i wont find blood untill 20 or so yards down the trail, so it is important to evaluate the surrounding trails, keep in mind a wounded deer is likely to travel down hill if it can, blood will usually be well above the ground (high grass, ferns, salmonberry etc) if it is really brushy. Just work very slowly.
Wehn blood is found, an evaluation must be done, Whats in the blood is important If you find foamy blood odds are your deer hasnt gone far (no reason to jump your trail) if the blood is real dark, it prolly wasnt just a flesh wound, you might find chunks or bone,hide, lung, liver in your blood all of which are good signs, if you find stomache contents, back off the trail and wait about an hour. Sometimes a good blood trail that is easily followed becomes skimpy, and spread out , do not let this discourage you, it may just be that the deer in question is getting low on blood, just make sure you dont ever walk past your blood thinking your deer will be dead a few feet up the trail, i am as carefull tracking a well hit deer as i am one badly wounded, cause in the end you just dont know for sure, anything can happen.
In my experiences toilet paper is far more effective than marking tape, in the dark even a dim light will make those little sqaures glow, while marking tape will not, also in many woods there is marking tape everywhere from timber sales and whatnot, fresh toilet paper is amazing, you can have a weak light shined on it and get a glowing effect, sort of like when you shine a flashlight on a vehicles lisence plate (it glows even if its well out of the lights effective range.