This is a very easy and simple trophy but it may take up a lot of time. As you roam around the lands of Skyrim you will encounter lots of books most completely useless but mixed among them are skill books which raises a specific skill by 1 level. In order to get this trophy you will need to find 50 different skill books which can only be used once each. The best way to do this is search bookshelves in dungeons, towns, etc for books that are more expensive then others, more often then not this will be a skill book. If you do this while going through the story or trying to achieve lvl 50 this should unlock by the time you are done if you search most chances you get.