A very easy achievement, especially if you plan on getting any of the achievements requiring you to beat the majority of the game. A large amount of the side-quests in the game require you to go to uncharted planets, so you will get this achievement early on. As soon as you land on any uncharted planet, the achievement will unlock. You don't even have to do anything, just land in the Mako.
Note: Therum, the planet you will find Liara on, does not count towards this achievement. The planet you land on must be optional for the story.