My personal belief: everything should come from YOUR head.
Even if others have ideas, I didn't let anyone influence me with my tattoos and I love them since they are truly unique. They were a product of constant sketching and designing for years and I finally got them when I was satisfied with everything that I thought of.
What helped me get an idea, was to picture the tattoo in my head. What's the first thing that comes to your mind when you think of a tattoo? Are there decorations, is there a scene behind it...and with that start drawing ideas. Doesn't matter if you can't draw, that's what an artist is for! Once you come up with something that comes from you, then all the artist has to do is stylize it for you into a tattoo