This video provides the simple process I use to blow out my in-ground pool plumbing as part of the winterization process. We live in Michigan with harsh winter weather, so it's important to protect the lines against freeze damage.
In the 15 years we've owned our pool, I've primarily used our old electric leaf blower to blow out the plumbing. The leaf blower provides a high volume of airflow which works great in knocking out the water from the lines. I've also used a shop-vac in reverse flow to blow out the lines, although it wasn't as powerful as the blower.
We have a fairly standard pool setup (main drain, skimmer, pump, filter and SWCG). We use our pump inlet to blow out the skimmer/drain, and a union fitting downstream of the filter to blow out our four return jets. During the process, I manipulate our 3-way valves to direct airflow at specific lines.