Depends on the type of blower....

A 2 cycle blower (oil and gas mix) I would empty as much of the gas out
and run it dry. (make sure to put the choke on when it almost out)
(there most likely is still gas in the bowl)
2 cycle gas is nasty when it gets old. Turns into tar.
Anywho, pull the plug and clean it up. Spray some fogging
oil in there and pull it over a few times. Grease the auger
bearings and any sort of linkage.

As for a 4 cycle unit, I would run it to warm it up. Then
drain the gas by emptying it from the carb (many carb bowls
have a drain on them) If not empty the tank as much as possible, put a

little stabile in it and run it with the choke on to empty it all out.
When its done, I would change the oil, pull the plug,clean it and put a
some
fogging oil into the cylinder. I would also then put some never seize

onto the threads of the spark plug while I am on it and put it back
together. When done, I would put the starter cord a few times and the
lock it in on a compression stroke to seal things up. (most manuals
tell you to do this too)

Greese up the unit and away you go. (again this depends on the type of
blower, 2 stage units require that you greese up the auger assembly
(greese fittings)

If the unit is only a year or two old, I wouldnt bother with the belts.
I would always have a spare set as well as a couple of shear pins
depending on the type of blower. (again single stage vs. two stage)

The ONLY time I would leave gas in the gas tank is when they are the
old ones made of steel. I would top it off to prevent rust in there.
Otherwise the newer plastic or aluminum ones dont need it.

One thing that most manufactures dont say anything about is spraying
all the exposed metal parts and linkage (around the carb) with a
protective lubricant spray (used on outboards) If it works on
protecting my outboard in salt water, it'll do GREAT in my shed!

Hope this helps.
Tom