10. Use the Level 25 Character Boost
If you've only played Destiny without any of the expansions, then your Guardians are probably lagging way behind everyone else. To get a jump start on The Taken King, be sure to use the one-time character boost on any one of your Guardians, or even a fresh character.
The boost, called the Spark of Light in your inventory, will bump your selected Guardian to level 25 and allow you to instantly access the expansion's content.
If you already have Guardians above level 25, then save it for a new character on a class you haven't yet played.