How to make my website display in the first page of google?

Google is mostly concerned about high quality websites linking to you and you not linking out to very many.
If you can find a way for your site to be listed on great sites all over the world, you should achieve a higher rank than you have now.  Your overall quality of content is important to Google , so it should be important to you.  The more users you have the better.  

You really need to take a look at what the folks listed #1 are doing and saying in the forum:
Make a list of what you love about it.
Make a list of what you hate about it.

Improve their ideas and make them your own.

As suggested earlier, what is the most important is content, content, content. SEO is just trying to give content all the exposure it deserves... but cannot achieve permanently high ranking with poor content.
If your forum has lots of good participants, then certainly this will generate good content and on the long run Google will know and tell.
How can you speed up things though?

1 - Having relevant metadata is certainly helpful. But the first point is to define which are the relevant keywords.
Is "australia forum" a relevant keyword expression for your content? This is an important question: depending on your content, "australia" might be (or not) more important than the theme of your forum. This theme is more probably the one for which you should try and claim some success on keyword ranking.

2 - Except if you have a strongly australian-local content, why would you want to limit your ambition just to australia when lost of people worldwide are speaking the same language as you do? If you look at success of some "companies" like Mambo or Joomla, you will see a strong worldwide presence, forums written 24 hours a day from all over the globe: very few people know they are australian born, and in fact nobody cares!

Ok, Google will never display a website on the first page just because you would like it to do that. You must have a lot o content related to the search keys and you also must bare this in mind:
- make a xml sitemap, the forum, if it is a forum you have might just have a script ready-made somewhere over the Internet;
- the Robots.txt will not help the site index but will prevent search engine bots in displaying contect that you don't want displayed on searches, like the admin page, some other system files etc;
- have the meta content dynamic with a script. if you are using a forum software you should find easy access to resources like SEO tools for Forum X;
- another very important aspect: try to keep the forum at a minimum level of graphics and javascript. Google doesn't like tons of js code in your source, so be careful what addon you attach;
- your forum must have many categories, many users, many topics and many posts with many replies. It sound difficult but it's not. If it's on the 3rd page you must have some content;
- you forum must have other sites linking to it. Subscribe it in a lot of online directories and portals;
- if you have basic html/php knowledge you can browse the forum's files and add title to all links, clear all comments, fix potential errors and shorten the code (use b instead of strong etc);
- bear in mind that Google likes fast loading websites, clean design, a lot o text, not to many photos (if you have photos use the alt attribute to specify the photo's content), webpage changes, update sitemap etc.
- subscribe and analyze your website with a SEO tool. Google offers https://www.google.com/webmasters/tools/siteoverview You may take a look of the WebCEO software, it's free to use http://www.webceo.com/ and it's a very powerful seo analyzer;
- promote the site constantly, Google checks your website in a 3 days cycle the fastest so keep it up to date and monitor it until it reaches 1st position. Your job is not finished then but if you are the 1st in Google on a general term like that you can relax, people will come and write on your forum without inviting them or promote the forum day and night. Stay focused on the content.

Hope you find this useful! It's the basic of seo.

It would help me to know more specifically which site is yours so that I can see what content is turning up on the 3rd page of rankings.  This is a simplified approach to everything my revered colleagues have suggested above.

Two things I think help with site ranking are:
A). A clean and concise "entry portal" that differentiate your site from the others likely to be returned when 'australia'+'forum' is searched, and...
B). Update the "entry portal" with a "Last revised on...(date)" line of simple HTML because many search engines "notice" (from what I am told) the frequency with which content changes, and...
C). If it is technically possible for you to do so show the "Top Five Most Active Topics" with at least a paragraph of their content in the form of a snapshot summary on the "entry portal" page; and rig this to dynamically update daily.  This keeps the content fresh and also (from what I am told) brings your content closer to the top of the rankings.

Disclaimer: Some of what I describe may NOT apply to Google specifically but may apply to other search engines.