The Introduction Course I attended with Emma Farrell in Bath gave me a great foundation for a good breathe-up technique. It essentially consists of 2 minutes of relaxation and regular breathing punctuated by short holds.
I try and imagine where the air is going when I inhale using belly breathing and the stages by which my lungs fill – first through the mouth and into the lower portion of my lungs, big belly comes out. When my lower lungs feel full I slowly begin to inflate the upper part of my lungs making a conscious effort to use the muscles in my rib cage to expand my lungs further. Before I feel uncomfortably ‘full’, I start exhaling from the upper part of my lungs finishing by tensing my stomach muscles slightly, squeezing air out of the lower lungs.
I found an excellent introduction to freediving on the DeeperBlue Forum posted by Akoni, which I signed up to the other day. There's loads of useful information in there and tips for improving technique for breathe up and other facets of breath holding. Enjoy