I cover the air hole with my finger and pull a few times only with a new wick/build, just to get everything started (building up the right amount of pressure to get the juice channels pulling juice up to my wick). After that, I will literally not need to do it again - unless I've used too much wick and have blocked the juice channels, then I might do it if I find myself getting dry hits. It has helped just shift things around a little to sort it out, but careful with it, as overdoing it will lead to juice filling up the chamber and making its way down the air hole, down the KFL, onto your mod... fingers... hand... clothes... floor... everything. Ugh.
Blowing though, like MadTz said, with the air hole covered just means you're forcing air into the chamber and into the juice channels, stopping the flow of liquid. Regular usage will get it back to normal in no time, but I can't imagine it's helping unless your chamber's flooded already (in which you're better holding the device upside down, having some tissue by - but not blocking - the air hole and then blowing to get juice out of the chamber as well as the air channel)