As other anons have mentioned, the main factor is scent. Chances are most deer will smell you and skit off without you ever knowing they were there. Don't bathe for a few days and leave your hunting clothes etc. outside so they smell neutral.
Purchase a small squeeze bottle like pic related and fill it with talc / chalk / corn-starch etc. then give it a squeeze to find the wind direction.
Read up as much as you can on tracking as well.
http://www.amazon.co.uk/The-SAS-Guide-Tracking-Carss/dp/1585740314 is a good start. It covers everything from animal tracks to night tracking and how old prints actually are.
