Answered[ Edited ]
Other posters provided great product suggestions; I just want to clarify that it is impossible to actually reduce the size of your pores. Everyone has them, and their size is determined by genetics. However, you can reduce the appearance of large pores with proper skincare. Per Dr. Perricone, pore size is proportional to the size of your oil glands (which is determined by genetics) -- and clogged pores, caused by acne symptoms, such as blackheads and pimples, are partly responsible for enlarged pores.
When a pore becomes clogged by dirt and bacteria, oil within the pore builds up, which causes the pore’s walls to dilate to make room. Acne symptoms appear when pores cannot expand fast enough to accommodate for this increase in oil; and once the pores expand large enough, acne clears up.
The two main contributors to large pores are genetics and age. In general, if you have oily skin, you will likely have larger pores, since the oil glands are more active and, as a result, need a bigger opening to release oil.
Since pore size is genetic (and you can't alter your genetics), it is impossible to shrink them. However, you CAN address excess oil and reduce the *appearance* of large pores by cleansing them of debris, excess oil and bacteria, which will help to stop them from expanding to accomodate build up -- and they will look smaller.
Again, you have been given great product suggestions -- I just wanted to clarify re: changing pore size. You can keep them clear with the products suggested, then disguise their appearance using primers, etc.