Some of us started playing the dulcimer back when there were no teachers around, yet we learned to play guided mostly by common sense and whatever musical ability we had developed on other instruments. And then we went on teaching others what we had already learned.
Pretty soon the rules started coming out: You MUST alternate hammers even if you have to stand on your head to do it! Right hand lead! Left hand lead! Look ma, no hands!
Then, as if that were not confusing enough, another question raised its ugly head: techniques first, or tunes first? I have a simple answer to that. It's the chicken or the egg conundrum. Let's say the egg is the technique, and the chicken is the tune. If you get the egg first, it'll hatch into a chicken. And if you get the chicken first, it'll lay the egg anyway. In other words, if you start with techniques, you will have to learn tunes in order to apply them. And if you start with tunes, the techniques will eventually follow.
The most common mistake folks make is to think that if they get an instrument and a couple of "learning" CDs, in a week or two they'll be good enough to play Carnegie Hall.
My advice to all who start on any folk instrument is to be patient, and keep playing. Realize that there are no bad habits to be developed by mistake if you follow one teacher instead of another. No teacher is a bad teacher. No one will set you on the wrong path. After all, a teacher is a player first. He must be doing something right!
You learn something from everyone. You take what you can, and move on. Eventually, your playing will become a distillation of the many things you've learned along the way -- and it'll be your own personal style. Then you can teach somebody else.
Or book Carnegie Hall.