Well as you would have probably guessed, PR can be increased by getting more backlinks for your page. The more backlinks and the higher quality they are the more your PR will be.
Here are some tips:

- Submit your site to directories.
- Write important content to your site that would make people link to you.
- Write articles and distribute them.
- Participate in forums (while adding your signature which includes a link to your site).
- Buy some links on high PR pages.

The following are some other factors might be considered by Google for calculating the PR lately:
<ul><li> Site age: The older the better, Google seems to like old sites.
- Backlink relevancy: Googles seems to be taking into account how relevant is the page linking to you, if it is not that relevant, the link won't weight much.
- Backlink duration: How long was the backlink up?