It's best if you have or can borrow a meat grinder. You really can't beat meat grinders for getting a smooth, uniform texture and making sure all the ingredients are combined. They make stand-alone meat grinders that clip onto your counter as well as attachments for KitchenAid mixers (see links below for sources).
Second to this, try using a food processor. Grind the meat by slowly pulsing the processor. You want the meat to get chopped without turning into a paste.
You can also simply buy pre-ground meats from your butcher, or ask your butcher to grind the meats for you.
To stuff sausages into casings, you'll also need some special equipment (usually part of the grinding equipment). You can use a pastry bag to fill casings, but you probably won't get the sausages quite as tight and plump as you would otherwise. Alternatively, you can simply form the sausage into patties and cook them like that!
The key is to keep everything cold, cold, cold. All forcemeats (of which sausages are one) are a kind of emulsion of meat and fat. If the equipment or the ingredients get too warm during grinding, the emulsion can't happen. Then when you cook the sausages, the fat will separate out instead of staying suspended in the meat and you'll end up with dry sausages floating in grease. Yuck!
Keep all equipment in the freezer right up until you're ready to actually grind the meat or fill the sausage casings. Also, make sure the blade on your grinder is very sharp. If it's dull, you'll end up smearing the meat instead of cutting it.
Chop all the ingredients very small. Cut the meat into small cubes and mince any vegetables. This will ensure a more uniform combination of ingredients.
Freeze the meat (and any other ingredients) before grinding until the cubes are hard on the edges but still soft in the middle. If you feel the meat is getting too warm while you're grinding, stick it back into the freezer for a few minutes.
Taste the mixture before stuffing the casings. Once you've stuffed the sausages, you can't go back and re-season the meat! Cook off a small patty of meat mixture now and give your sausage a taste. Adjust the seasonings and re-taste as needed.
Chill the meat mixture before making sausages. Repetitive, yes, we know. You'll thank us when your sausages turn out juicy and flavorful!
Once made, stuffed sausages or sausage patties can be frozen until you're ready to cook them off. It is possible to cure and smoke your own sausages, but we'll save that particular ball of wax for another post.
Recipes and Other Tutorials
• Sausages, Sausages, Sausages from To Be Mrs. Mary - a good basic recipe along with some fantastic photos showing the whole process.
• Homemade Sausage Recipes from The Spicy Sausage - There are more sausage recipes on this site than you will probably ever need!
• Sausage Making Tips from Lesley Cooks - More tips and advice on cuts of meat to buy and how to stuff casings
• Sausage Making Tutorial from Sausage Mania - They're using industrial-grade equipment that most of us don't have access to, but check out their photos of stuffing sausages for good basic technique.
• Sausage Making Supplies from the Sausage Source - This company sells things like basic grinders and casings. We're also lusting over their smokers...
Before leaving you to sausage-making bliss, we want to point out that although we're talking specifically about sausages in this post, these guidelines also apply for making any kind of forcemeat. If sausages are a little beyond you at the moment, other forcemeats like terrines, patés, and even meatloaf can be a good stepping stone.
Watch for one more tutorial on sausage and sausage-making a little later today. What other sausage-making advice do you have to share?
Related: Food Science: How is Meat Cured?