yes, for very less competitions you can gets the rank or manage to improved your SERPS with Directory Submission. but if your key words with very high search volume directory submission is not enough for you.
So what else can be done besides backlinking to show google we are an authority site, because in reality our website has been around for a long time and we are number one in what we do, but obviously the trick is to let google know we are number one.
What do you mean here by telling that to rank on top on Google we need to 'become an authority is our niche' ? Please explain it.
Start to directory submissions and social bookmarking that will drive a volume of traffic to your sites
If you can make the effort to submit an ORIGINAL blurb for your submission, it will go a long way to making your backlink more effective. Indeed if you can come up with a unique overview of a few paragraphs you may even see the directory listing itself indexed.