Jan Rabe - Technical Team Lead Native Apps

HEAD is a pointer to a commit (usually master) so when you checkout your repository the commit which HEAD points at will be checked out. Usually you'd want it if when checking out you want a different branch or tag to be checked out.

You can take a look at what it's pointing out by issuing the following command:

And you'll probably see something like the following: origin/HEAD -> origin/master

You can delete HEAD if you don't need it (although it doesn't do any harm being there) by issuing the following command: 

Note: on github there is already an checkbox you can check under Settings > Options.

The two following medium articles are explaining the best strategy

Tips for exporting vector assets from Sketch to Android
Design best practices for Android mobile App (with SketchApp)

• Avoid using masks - they're not supported
• fill rule: ‘fill-rule:evenodd’ is not supported
• transforms on path are not supported, use option Bake transforms into path
• avoid groups
• avoid rotations
• Make outlines, not strokes
• Pathfinders are your friend
• Adobe Illustrator is the best troubleshooter
• Combined and transformed shapes may not appear as what they seem
• Transparencies are your friend...
• …and gradients are not
• Export artboards, not layers
• Flattening shapes will solve most problems
• If your shape has a border, use an centre border
• Text directly are not supported - text need to be converted to curves
  
  Bonus
• try out vector optimization tools, e.g.  svgo-compressor or avocado