Need help on SEO

Hi guys,

I want to rank on words

" PVC Stolarija Krusevac " ,, " PVC Stolarija Nis " and " PVC Stolarija "

I'm already on Page 2 on " PVC Stolarija Krusevac " but I know I can do it better!
I know it's not difficult.. but I'm still newbie so I need some suggestions on how to start..

P.S : It's on Serbian.

Thank you guys!