Everything I've read says that once pores are enlarged, you can't shrink them, so any products aimed at pores can only reduce their appearance, they don't reduce the actual pore size.
I think that Clinique's Instant Pore Perfector is the best cosmetic products I've tried for pores (Benefit's Porefessional, which is very popular and the same price, I don't like, as it wears off quickly). I use it after I've applied my other liquid products, i.e. moisturiser and foundation and before powder. I tap it over my makeup, rather than rubbing it in, wait a minute, then press on powder. Makes pores disappear and they stay that way until I take my make up off.
I agree with OP re Clinique. Product doesn't reduce or prevent pores but minimises look of them. I personally use Clinique pore refining solutions serum which I love. It acts as a primer and foundation goes on smoothly. It's very pricey though - £53. .00 BuT it lasts ages and I bought it on Clinique Bonus time in Debenhams so I got free gift (really good variety of products plus good size products ) and bonus beauty clubcard points .