For a basic and readable introduction to spey casting methods, techniques, and terminology, please see Bob Pauli's free, downloadable spey casting instruction booklet -- available in both English and Spanish.
For spey casting sink tips, we have seen phenomenal recent advances: Skagit head lines (RIO and Airflo), special-purpose rods (Loomis, CND), and Skagit-casting techniques (McCune, O'Donnell, Ward). While these advances have made spey casting sink tips easier, they also present a potentially confusing array of options for the angler.
At the Golden Gate Angling and Casting Club, we have experimented extensively with the new Skagit lines paired with a wide range of sink tips and Spey rods. We've also fished them extensively -- primarily for steelhead on the Babine, Kispiox, Bulkley, Skeena, Dean, Situk and Deschutes. What we've learned, from our practical anglers' perspective, may make your fly fishing simpler, less costly, and more effective.
"Half Out and Go" is the easiest method we know for casting sink tips, especially those longer and heavier sink tips that are challenging to cast with traditional Skagit casting methods. Casting sink tips is made even easier by using good setups.