Off page SEO for internal pages has one main difference. The methods involved are the same as normal, generating backlinks and web presence through marketing etc.
The difference is that your focus will be more content specific. For example, say you have a camping website, for the 'Tents' page your off-page SEO will deep link directly to this page, mirroring the keywords on that page and in the title, meta desc, etc. For the 'Sleeping Bags' page your off-page SEO will deep link directly to this page, mirroring the keywords on that page and in the title, meta desc, etc. So this differs from the home page of your site which is focused on 'Camping'.