For any of the HD models, it is very important to properly and regularly lubricate your printer. This will help your printer last longer and generate better quality print. We generally recommend applying new lubrication about every 100 printing hours. Doing more than enough is better than not enough. Not adding additional lubrication can permanently negatively affect your printer. This includes excessive wear to rods and misalignment of the printer.
The grease used is called "White Lithium Grease". It can be purchased at any local hardware store. It will be used for the smooth and threaded rods (6 for the XY, 3 for the Z).
Be careful not to get any on the acrylic frame panels.
Here is a link to purchase the White Lithium Grease.