Google Dancing Question !

Hello there

I have a website, a blogpost to be more exactly.
I had for a month,i target a long tail keyword with it,i've done some unique content,social bookmarking,etc.
I was indexed in google with a post that i`ve written on 1 july,the thing is that i made some new post on the home page thill then.
Questions are : 1 : After your blogpost homepage created let's say on 2 of july is indexed,you need to write new content on another page of your blog? or you just add new content on the exact page.I ask this, because i;ve added new content daily to my homepage and also secondary pages,my site is now in google dance,i find myself on the back of the pages 40 etc.

For question 1 , to be more specific , i just want to know if it matters if i update the indexed page , does it matter? Because it's a blog, i just need to use in same article my targeted keyword? If i do this is ok?

Question 2 : I saw also that my competitors are not on the page they`ve used to be.It's not because of my updates ? does just google re-order the competitors?

I must mention that i was on the second page of .com , first page on canada, first page uk etc.

Thanks you for your answers