Blueberries take quite a long time to fruit (compared to other soft fruit, I've found), my 5-year old bushes are just getting into the good-quantity-of-fruit category.
To lower soil pH
- you can add sulphur dust or chips to the soil, microorganisms in the soil convert this and make the soil more acidic- can take months though
- dig the plot out and add ericacious compost
- add peat and moss (peat bogs are where blueberries are originally from- nice acidic soil, though with the destruction of peat bogs this might not be a good plan)- again takes months to break down and have a difference
I did a mixture, got some ericacious compost for 10c a bag at a closing down sale, dug in lots of conifer needles and moss and left it to break down for a year, and added a spinkle of sulphur for good measure- i went from pH7 to pH5.5 (how long this wil stick around for- we shall have to wait to find out!)
Blueberries don't seem to have very deep roots, so you might not have to go very far down with your acidifying efforts.