yeah i am facing it as well. I think it is normal. Its a fact that a lot of competitors are working hard on their sites to make them stronger and best. This thing causes the keyword to fall down. I think you should focus on the quality content, back links and SEO of your site.
I agree with RjMaan. And also, have you performed adwords competitor analysis? It’s a very important step to understanding your competitors, you really shouldn’t skip it… If you need help, let me know.