Annoying blackheads (AKA comedones/open comedo) and enlarged or open pores are a problem for lots of people - in fact it's possibly one of the most common forms of acne that most people have at some stage in their life. Keeping blackheads to a minimum is really all about consistent maintenance as there really is no miracle potion that keeps them at bay permanently.
A blackhead is an open comedo and they appear when excess oil and dead skin accumulate in the sebaceous glands duct. The main substances found in these ducts are keratin and sebum (an oily secretion of the sebaceous gland) which darkens when it oxidises which causes the black appearance (some people wrongly think its dirt in the pores but its not at all - you could clean your face for an hour solid and the black will remain black) Blackheads often occur in the hair follicles and clogged hair follicles reflect light irregularly to produce the black hue.
To try and understand why you get blackheads and enlarged pores try to imagine a tube and picture oil trying to come up to the surface to protect and moisturise your skin but there is dead skin stuck in the top of the tube preventing the oil from escaping which then causes the tube to swell meanwhile the amount of oil being sent up the tube continues to increase and so when the diameter of the tubule dilates it can give the appearance of enlarged pores and or blackheads if the sebum and keratin are stuck on the surface. This is what leads to that 'orange peel' look around the nose and inner cheeks - it usually only appears on the T-Zone part of the face as these tend to be the oiliest areas.
So once you understand what causes the problem its easier to see what you can do to help solve it. For a start exfoliation is crucial - if you don't make an effort to slough off those dead skin cells then chances are the pore will become clogged. Your glands will always make oil and send it to the surface - that's what a good gland does and its not a bad thing - its a natural protective barrier and moisturiser for the skin and so you need to try and make sure it can make it all the way up to the epidermis with as little clogging as possible. Getting the right kind of exfoliator for your skin type is important though as some are far too rough and grainy for sensitive skins and being too rough when scrubbing can cause broken capillaries and little skin tears so be gentle and avoid the very thin and delicate skin area around the eyes - I made this mistake once and actually ended up with little bruised looking marks around my eyes - this skin just isn't thick enough or tough enough for using anything rough so focus your attention on the T-Zone instead.
Some other things you can try out are using a suitable toner after cleansing and exfoliating to try and close the pores after you've cleaned and scrubbed them. Personally I would suggest a mild Witch Hazel product (dilute if need be) or Burts Bees Acne Solutions Clarifying Toner and unless your skin is oily all over just use it where you need it (nose and chin being the most likely places) you don't want to risk drying out other parts of your face unnecessarily. Products designed for the T-Zone with ingredients like Salicylic Acid are also great for acne prone skin and I find much more gentle than products that contain Benzoyl Peroxide which I think tends to be much too harsh and dries out the surrounding skin and causes flaking and redness and sometimes hurts too - Not good!
Some people also suggest that another effective ingredient is Retinol A (Vitamin A) which is also a well know anti-ageing ingredient, but word of warning - a lot of people with sensitive skin (like moi) will find Retinol A products quite irritating on their skin and so may not be the best option for all. Another option to try maybe once a week or so if you feel your skin is very oily/shiny looking in parts, is a mud/clay mask to draw out the oil and other impurities but again remember unless your face is actually oily all over only apply to the T-Zone or where needed - these masks can be very drying if used on skin that doesn't actually need it.
And my last tip is for preventing enlarged pores turning into big old enlarged spots - if you happen to notice an enlarged pore that's starting to look a bit pink and raised and you think its likely to turn to a giant angry volcanic spot of biblical proportions overnight (the horrid cystic variety) just in time for your girls night out/big date/job interview (insert appropriate exciting event here) then dab some tea tree oil on it immediately and try to remember to keep doing it every few hours if possible and it should stop it in its tracks if you get in there early enough. Boots happen to sell one that's good value called Thursday Plantation Tea Tree Oil but you can find topical Tea Tree Oil pretty much anywhere (chemist/health food shops) - just make sure you get the kind suitable for skin and not for aromatherapy.
Oh and remember hormones greatly affect the skin so when
its that time of the month these problems are likely to be much worse so
its even more important to make sure you are vigilant about your skin care routine both morning and night and if nothing topical seems to help consider asking your GP if he can prescribe anything - in particular a change in pill type can often make a huge difference in controlling hormonal acne.
Hope that explanation made sense and the advice is helpful - If not, leave a comment with a question and I'll try to explain better :D