Remove the glow plug and look at it with the igniter connected. Do this in a dark place. The glow plug should glow bright orange. If it is totally dark, it may be burned out. If it barely glows, your igniter battery may be low. Also look at the element. It should look like a small spring.

Are you using an electric starter or flipping the prop by hand with a stick? What engine? Is the engine popping at all?