I've read the whole Bootstrap 3 documentation. I learned a few new things.

learnings.md

• add respond.js to IE < 9 https://github.com/scottjehl/Respond
• make sure we use latest IE renderer available <meta http-equiv="X-UA-Compatible" content="IE=edge">
• http://getbootstrap.com/getting-started/#support-ie10-width
• <meta name="viewport" content="width=device-width, initial-scale=1">
• .container > .row > .col > .row > .col
• make semantic col names: http://getbootstrap.com/css/#grid-less
• Learn
  • text alignment classes: http://getbootstrap.com/css/#type-alignment
  • .form-group with .has-feedback: http://getbootstrap.com/css/#forms-control-validation
  • http://getbootstrap.com/components/#list-group
  • http://getbootstrap.com/components/#panels, I like the combination with tables
• use <footer> in <blockquote> for citations. Also: .blockquote-reverse for right-aligned
• Lists
  • remove list-styles by adding .list-unstyled
  • .list-inline for inline lists
  • Horizontal description lists with .dl-horizontal
• use kbd for for keyboard shortcuts
• Forms
  • .form .form-group :any(.label, .form-control)
  • for .form-horizontal, form-group behaves lik .row
  • wrap checkboxes / radios into <label>. And wrap these <labels>s into div.checkbox / div.radio
  • for inline, wrap in div.checkbox-inline / div.radio-inline
  • .form-control-static to add text where you'd otherwise put an input
  • .form-group can have .has-success / .has-warning / .has-error
  • hide labels with .sr-only
  • control sizes of .form-groups with .input-lg and input-sm as well as .col-lg-*. For .form-groups, there are form-group-lg and form-group-sm
  • .help-block for help text
  • Buttons: .btn-lg, .btn-sm, or .btn-xs
• .img-responsive to make images max-width: 100%
• .img-rounded, .img-circle, .img-thumbnail
• .pull-left / .pull-right can be used everywhere to float content
• .center-block
• .show / .hidden / .invisible
• .text-hide for image replacements
• .visible-sm-*, .visible-md-*, .visible-lg-*, .hidden-xs, .hidden-sm, .hidden-md, .hidden-lg, .visible-*-block, .visible-*-inline, .visible-*-inline-block, .hidden-print, visible-print-block, .visible-print-inline, .visible-print-inline-block

I knew half of this already :)