There is a Sharepoint  connector that works for some simple migrations that can be enough so start by checking out that. You can trigger a manual update between the two systems to transfer documents and site pages etc.

http://world.episerver.com/add-ons/Connect-for-SharePoint/

If you need a more advanced one time migration I would build a new import class on the Sharepoint side that uses Episervers rest api to create content and media. If you haven't got the possibility for using the rest service I would export Sharepoint content into xml and then build a custom scheduled job on Episerver side to import them. Hope that gives you some working option.

Check out service api for creating content in Episerver here 

http://world.episerver.com/documentation/Items/Episerver-Service-API/