More formal:
* I adapt readily to new information and skills.
* I possess a strong capacity for rapid learning.
* I am adept at acquiring new knowledge and skills.
Less formal:
* I pick things up quickly.
* I learn fast.
* I'm a fast learner.
* I grasp new concepts easily.
Focusing on results:
* I have a proven track record of mastering new skills efficiently.
* I consistently exceed expectations in learning new tasks.
The best option will depend on the context. For a resume, a more formal phrasing is generally preferred. For a casual conversation, a less formal option works well.