Get an exfoliating body scrub and use it about 3 times a week on the problem areas in the shower or bath (stand up if you bathe rather than shower) It's really effective and gets rid of all the dead cells that cause blackheads to form. In fact you might as well use it on your whole body regularly to prevent blackheads and dead skin cells building up.
I use a palmolive smoothing sugar scrub which smells lovely and works quite well. Dove also do one which is really creamy and great for dry/sensitive skin. Clean and Clear do a spot fighting body wash too.
Also to get rid of any remaining blackheads...when you're in the bath/shower and your skin is wet and warm (so your pores are open), squeeze them out with your fingers. Easy peasy.