Start with endgames: first 3 men, then 4 men, then 5 men. Learn the 5 basic checkmates: KQ vs. K, KR vs. K, KBB vs. K, KBN vs. K, KNN vs. KP. Learn basic endgames: KP vs. K, KQ vs. KR... A good book is Chess Fundamentals - Capablanca. It contains all you must know.