How to get more indexed from Google?

Hi all,

I have a website with more than 30,000 records in database and I launched this website 2 years ago. But the amount of indexed links are not stable. At the best time, Google only indexed about 18,000 links and normally is 4,500 links.

I did all ways that I know as submit sitemap, build back link but I can't force Google index more.

So the question is how can I force Google index more links in my site? (using tools or other method)

Is the db content unique? If not, this may be part (all?) of the problem.

Getting some deep links may help (Backlinks to deeper parts of your site.)

If people cant browse your site with minimal amounts of clicks neither can bots. If its a forum dont have too many sub sections for example