Most people tend to be afraid of elemental sulfur, but they shouldn't be. It is one of
the best methods of acidifying the soil, yet it is surprisingly gentle
and is usually considered to be an organic gardening practice. I buy it
in 20 pound bags on Amazon.

Yes, you should use pine mulch,
compost and similar things, when available. You should also try to
amend you soil to try to get a sandy loam. However, once you have done
all of that, you probably will STILL need to acidify the soil more. But also keep in mind that your soil will CONSTANTLY be trying to gradually revert to its normal pH.

Blueberries
like a pH of 4.0 to 5.5 or so. This is definitely an acidic soil level and
is very close to the acid level of apple cider vinegar. Meanwhile, most
people have neutral soil, in the range of 7.0 to 7.5, and, if you live
near mountains/hills or lakes/rivers that contain limestone, your pH for
both soil and water will probably run in the range of 8.0 to 8.4.
Blueberries might possibly barely survive, but will never do well in
such soil. So, you must acidify it.

ONE POUND of yellow,
elemental sulfur powder mixed into the surface inches of 100 square
feet, will drop the pH by 1.0 points over a period of about a 1 year.
It works because the action of soil bacteria, along with moisture and
warm temperatures, allows the soil bacteria to gradually convert the
elemental sulfur to sulfuric acid, and this acid is never really free,
but it neutralizes the limestone and alkaline components. So, 4 pounds
of sulfur in an area of 10 x 10 will often drop the pH from 8.0 to 4.0
in a year or so. But the soil, and water, will push back, especially if
the soil is derived from a moderate amount of limestone. The limestone
contained in the soil continues to dissolve and will work to bring the
pH right back up. Around here, we need to use 5 to 10 pounds of
elemental sulfur in such an area, in order to get the pH down to an
adequate level.

In addition to the above mixture of sulfur with
surface soil, if you soil is on the alkaline side, like ours, mix TWO
whole cups (1 pound) of sulfur with the dirt in the planting hole, at
the same time as you plant the blueberries.

Please note that
these instructions are for using ELEMENTAL SULFUR, which is generally a
bright yellow powder, AND, it takes time to work (a year or more), AND
you need to keep reapplying sulfur to the top of the soil at a rate of
1/2 pound to 1 pound per 100 square feet, every year or two. I
also went online and bought some simple electronic pH testers for around
$20 or $25 dollars each. When I want to test my soil, I mix some soil
with DISTILLED water (available at most grocery stores) and use the
tester on the resultant runny mud mixture.