See Also

Trailhead has a nice overview of Page Layouts https://developer.salesforce.com/trailhead/force_com_introduction/customizing_user_interface/ui_page_layouts

Page Layout Notes

Different Layout Types

Compact Layouts are for the Salesforce Mobile App. Mini Layouts are for Hover links and the Console.

Compact Layouts

https://help.salesforce.com/HTViewHelpDoc?id=compact_layout_overview.htm&language=en_US

https://help.salesforce.com/HTViewHelpDoc?id=compact_layout_notes.htm&language=en_US

Custom Buttons and Links

Trailhead has a nice overview https://developer.salesforce.com/trailhead/force_com_introduction/customizing_user_interface/ui_nav_buttons_links

The Stack Exchange questions at Make a button on a layout be visible only to a specific group of users have some great suggestions for buttons and links too. 

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