The page rank is a representation of how well your website is optimized and how popular it is. There are lots of factors to take into consideration when aiming at increasing your page rank.
First of all, you have to have a better than average on-site Search Engine Optimization (SEO), that way search engines will be able to better understand the content on your page rank and in turn show it to users who will be the most interested in it. This includes a lot of planning on which keywords to optimize your site for, placing these keywords appropriately, having a quality meta title and description for your page, and most importantly a ton of quality content.
Moreover, the age of the web page is also of importance, as is the number of times a search result related to your website is clicked by visitors. Having lots of traffic and generally being a popular site has got a huge effect on the page rank search engines will attribute to it.
Lastly, the number of links both to and from your website are pretty important too. Having lots of links on your site, pointing outside and internally, is viewed favorably by the search engines, as this is a sign of a sound informational network which is beneficent to their users.
As a whole, increasing you page rank is a natural process which takes time. And when you create a lot of interesting and quality content oriented towards your visitors, you will be surprised how quickly you will build your page rank up.