Here are some obvious answers:

1) Run a Google AdWords campaign to drive views to your video through the 4 different paid ad options for YouTube videos
2) Run a Facebook ad campaign
3) Run a StumbleUpon paid discovery campaign
4) Submit / share your video to video curation sites like
ShowYou
5) Send out an email campaign promoting your video (or partner with someone that has an established list)

Here are some less obvious answers:

1) Annotate your other YouTube videos and/or get other YouTube Channels to add annotations to some of their highly viewed videos
2) Have your video posted on popular Facebook Pages and pay to promote the post
3) Submit your video to social groups / communities (e.g. Facebook Groups, LinkedIn Groups, Google+ Communities, etc)
4) Create a landing page on your site, embed your video and optimize the page around a keyword theme to get the page to rank organically for relevant key phrases
5) Find influencers on Twitter (using a tool like Followerwonk) to get them to post your video on their social channels