My Google SERP down how to get back

SERP is a term webmasters use it is search engine ranking position some time when you see that a good traffic is coming from a keyword and after some days you see that now traffic is decreased with that keyword
sit back double check your self.
Your content is fresh and unique?
You have not copied it from anywhere
You have more competitive ?
Your backlinks down or up ?
Page Rank (Google webs sites ranking system) down ?
You make some mistakes when optimizing your site with search engines
The reason is you are sleeping and as a result you Google SERP down
wake up
Suppose that you went on a shop to buy a fresh Piza you bought it and after some days you go again there you see no changes there every thing is same as it was before what thing ll come up in your mind when you decide to buy another piza it might not be fresh
But if the shop was constantly changing and new promotions were always on, you would keep returning to see what else they had.
so make some changes advertise your website with some new ideas always build only quality back links do not run behind quantity
show some new trends make something new and you might get back your SERPS and also some extra that will be bonus