The first time I tried to make a pate, I was terrified. I was sure it was going to use expensive ingredients, and I would mess it up! So I shakily took out my Fannie Farmer Cookbook, because I had bought a pork butt on sale and didn't know what to do with it. A pork butt is about 1/3 fat, which is what you'll need for a good meat pate or terrine.
The first thing to know is that a pate and a terrine are exactly the same thing--the only difference being that a terrine is in larger chunks. (Pate is simply the French word for "paste," so I remember that pates have to be ground to a fine paste.)
Now that we know what pates and terrines are (that is, stuff ground up together), we can start thinking about how to make them. There needs to be some sort of protein to bind everything together: milk, fat, meat, eggs, cooked beans or other legumes. Everything else is up to you! Grind everything together, coarsely or finely, and pack it into a greased loaf pan. Bake for at least 20 minutes at 350 degrees. For meats, bake until when you prick it with a fork, the juices run clear. Let cool, unmold, slice and serve.
You can dress up those pates and terrines to make them more attractive. Consider putting a half avocado in the middle of the loaf pan and packing the rest of the pate around it. Add whole, or chopped bite-sized, pieces of something (nuts, for example). Roll the finished pate or terrine in chopped fresh herbs or sprinkle them over the top, or wrap a meat pate or terrine in bacon before serving. Instead of a plain loaf pan, use a fancy metal mold. Serve your pate or terrine on a bed of something.
How do you determine what goes together? That's easy -- taste! Use the ingredients you already know from another dish. (After all, a lot of Tex-Mex food is the same ingredients, just different presentations!) Or take a look at your refrigerator and pantry and think about what each item tastes like, and what would the other items taste like with it? You may find some real winners!