Echoing iSign's earlier comments...
I think that in order to become a better designer (and a better sign designer) you need train yourself to evaluate and analyze design - to look at what works (and why) and what doesn't work (and why) - and to practice deconstructing and reconstructing designs to understand how various design elements work together.
For example, take Neato's inspiring design and look at what works and why. I'm not a designer but I can still look at that design and recognize a few qualities that work and that I might experiment with in my own attempts at design, and/or would want to research further:
Those aren't your average free windows fonts. Where did he get them, why did he choose them? How do they work together? Where could I learn more about selecting/combining fonts?
Colours. Cooler colours to the back, warmer colours to the fore. Do those colours work together? Why? How could I learn more about how to choose and combine colours?
Movement. How do I read that design? Where do my eyes start, where do they stop? What's the lasting impression? In this case, I'm not reading left-to-right, but more top-down.. starting with "Graphics", then ending on JM. I actually take the time to take it in twice, which is unusual. Why? "Graphics" is dominant: Display font, largest word, and warmest colour pushes it to the foreground. But there's more than just that at work. There's the background shape. And look at the "gradients" (including rule/line spacing in the blue) and the way they blend with outlines.
You get the idea. I'm sure some of the trained eyes here can expand and improve on (and probably correct) my analysis. But you get the point. So what can you take from that and apply in your own design attempts? Or - better yet - let's see some analysis of John Deaton's equally inspiring design, and some attempt to apply that to your own attempt.