The first step in pore maintenance is healthy, clean skin. This would include washing, toning and moisturizing your face everyday twice a day. It also includes receiving a facial treatment at least once a month with a masque and extractions. If your budget doesn't allow for a professional spa facial, I suggest (and urge) an at home treatment monthly with a spa treatment once yearly. Your at home treatment should include a diatomaceous earth masque and Biore Pore Strips for extracting. I don't recommend manual extraction of pores at home as that can lead to scarring.
Second - Have patience. Enlarged pores are not something that can be reversed overnight.
Lastly - If you don't have patience or are not seeing any noticeable difference after 6 months of proper skin care, there are products out there that can help minimize the appearance of pores.
Clinque makes the widest range of pore minimizing products. From an emergency masque to a silicone based minimizing cosmetic, they are my first choice in pore maintenance.
Murad and Cle De Peau also make rather effective pore minimizing solutions.
Whatever your choice of product, clean skin and a healthy attitude are your first lines of defense. And don't forget your sunscreen!