The verse of this Nirvana song provides great fodder for practicing the really basic progression of E minor to G major. The "chorus" contains some slightly more difficult chords - barred chord shapes like C#major and F#major - as well as some quicker chord changes, but none of this should be too difficult with a little practice.
The strumming for "About a Girl" is somewhat unstructured - Kurt starts the song by strumming a "down, down up down up down up" pattern, followed by three bars of down up down up down up down up. This isn't a pattern Kobain sticks to throughout the song though - you should feel free to treat the strumming pattern as a guideline rather than as a rule. As is the case for many of Nirvana's songs, the guitar is tuned down a half-step to Eb Ab Db Gb Bb Eb.