I am sorry to give a useless reply but I think the answer is "it's hard".
That's why dead reckoning is not half as good as they make out when they teach it in the PPL (while slagging off GPS)
IO540, What mad_bear is descrbing is called pilotage, not dead reckoning. Learn your stuff before you slag it off.
mad_bear. Pick things you can see from a distance. Pick things you cannot easily mistake for something else. Don't pick things where there are two of them close together. When picking landmarks, plan so you can see your next but one landmark before you get to the next landmark. Pick landmarks where two lines cross eg motorway intersections. Quite simple really.