The use of different FACE makeup brushes (pretty self explanatory), My favorite is the mineral powder brush (Sephora #45), Its great for a full coverage foundation, easy to blend, no streaking. For a more Sheer coverage i suggest M.A.C 187 stipling brush and also M.A.C 130 (pictures not shown)
Perfect tips. One thing I must add: For those who have red tints to their skin and cannot find a green-based primer, use a yellow concealer! Place on red areas or acne scars and blend well. Let it dry, then add your foundation over the top and blend. Voila!