When putting on your liquid foundation apply immediately after your moisturizer; this will help your foundation smooth out, and slide over those pores without leaving streaks. Always start in the middle of the face and work your way towards towards ears and neck.
When using powder foundation be sure your face is completely dry, use a powder foundation brush (this brush is bigger), apply in a circular and down motion starting in the middle of your face working your way out to the edges.
Whether you are using liquid or powder always apply in a downward motion - never go up. However, with moisturizer it is just the opposite, always go up.