I don't do anything special, the flocking I bought came from China, in pretty large amounts and works out much cheaper compared to some of the smaller amounts you buy specially for modelling.
Here's the tools I use for the flocking, and along with some regular PVA white glue with a few drops of water added, if I'm doing a floorpan I will do it in around 4 sections, the boot liner was done in sections, floor, sides etc, I always airbrush the floor or the part I'm flocking in a colour that's very near the shade of the flocking I'm using, once dry the PVA glue is applied then the flocking is places into the sieve, and simply sprinkled over the glue, pressing down gently with my finger, the wooden stick is used to press the flocking down in the corners, and then left to dry for a few hours before moving onto the next sections to be flocked.