I am new to programming and have installed and setup Mavensmate with Sublime text. Please advise what's the command for previewing a visualforce page, the equivalent of preview button on the visualforce page editor on developer console.
There is no such functionality in sublime or Mavansmate. Sublime is only a text editor which has no direct integration with Salesforce.
To use Sublime preview a web page, you can take a look at this link. However, I don't think it will work for VF page though because the browser itself won't be able to understand those VF tags.
However, I don't think it is really a bit deal to me. To view the page, simply type [Your domain].salesforce.com/apex/[Your VF page name] into the browser, add you will be able to review it. Personally, I found it much easier to use than the preview button because you can add as many parameters as you want.