I'm sure it's been said here, but when i start a new puppet, the first thing I do is about three or four drawings of the character. they don't have to be GOOD drawings. its just an exercise to help envision the character before I start building and cutting up expensive materials!
You'd be amazed at what simply sketching out an idea can do for you. It really helps to start the building process in your head. It also helps to understand the geometry of the character's body. A long thin tubular body is a whole different affair than a round, bulbous body... so that gets you started thinking about HOW you're going to actually build the structure.
Being familiar with hand-stitching and machine stitching and the relative merits of both is another first step.
Getting familiar with foam, hot glue, fleece, etc. is another step.
I know how frustrating it is to have somebdy tell you that the way to do what you want to do is to start someplace else, but the puppet building thing is a process. Most people can't just pick up in the middle of that process without getting hoplessly turned around. Some can, but vey few.
-Gordon