Step 1: Get your meat:
Meat tends to taste better and be better for you (your soul at least) when it is locally farmed. If I could afford it I would always buy my meat at Prather Ranch Meat Company: www.prmeatco.com
located in the San Francisco Ferry Building. When you are cooking nice cuts of meat, try to find a place like this.
However, we are making sausage. I bought my meat at Safeway.
Sausage makers around the world are going to cringe at my meat choice, Pork & Lamb chops. That's because sausage is traditionally made with the little bits and scraps and fat and "parts that won't sell" left over after butchering. Unless you're a butcher or hunter traditional sausage scrap is hard to find.
The ratio I'm using is 3 parts Pork to 1 part Lamb. I tried to pick the fattiest cuts of meat I could find shrinkwrapped in Safeway. Honestly, really, go for the fattiest you can find. Production Pork in the U.S. has become so lean it's hard to even find Pork that has any untrimmed fat. In a traditional sausage half the scrap that went into it would be fat.