When it comes to Office 365, you may not want to have some of the links enabled at the top such as Yammer, OneDrive, and Sites. Although, I don't recommend disabling them. Sometimes you just aren't ready or there is a business reason preventing you from showing those links. These settings creeped into Office 365 a while back, but I still have people ask me about them from time to time, so I thought it warranted a quick blog post.
These settings can be changed by your Office 365 Global Administrator by going to the SharePoint tenant administration site. Click on the Settings link and you'll find the options to show and hide the OneDrive for Business, Yammer / Newsfeed, and Sites links.
Hide the links that you don't want to show and then click Save at the bottom of the page. Once you save your changes, you won't see the navigation change right away. It seems to take about five minutes. It seems to be cached per user as well. Just be patient and the changes should be made.
If you want to customize any of the other links in SharePoint (or add your own), you'll have to revert back to customizing the master page. It's not ideal, but it's possible.