You can use a few different tactics with Dragonite but my personal favorite is the Multiscale-Haban Berry Technique. Since Dragonite is an overused Pokemon, a lot of teams are prepared to take care of this guy. Multiscale is a great ability to take care of super effective attacks. It lowers the super effective move by a significant amount, but only when Dragonite is at full health. Haban Berry also helps decrease the damage of super effective moves against Dragons.
If you’re looking to preserve the Multiscale ability for further use, perhaps using leftovers or having the move Roost will help do the trick.