I am sitting here right now looking through a bead catalog with my mom and am finding that I am a bead snob. She keeps asking, "isn't this pretty?" and I find that if it doesn't fit into what I would buy, I can't help but think, "no, it isn't." I have carved out a niche for myself and I like it. I guess my advice to new jewelry designers would be is to know what you like. Having someone else pick things out for you rarely works because design is such an emotional experience. You have to be moved by what you are working with. I decided that I wanted to work with only natural stones many years ago because I needed to limit what I was buying. I have found now that, except for pendants, I can't work with anything else. It's okay if it's dyed, it just can't be glass or plastic.
I guess you have to be a snob in order to find your niche. I am also really picky about which clasps I use because if the jewelry buyer is in my life and I chose a hard to use clasp, I hear about it every time I see them. I have done much research into what I like and what fits all of the requirements of my frequent buyers' preferences.
When you are designing a piece there is a lot more to think about than just does it look good. You also have to think about what would someone wear with it? If you can't picture it on a neck or a pair of ears making an outfit better, maybe rethink your design. Just remember, you aren't just creating art, you are creating wearable art, it should be both.