My niece is about to turn 16 and her birthday is December 20 so I'm going over to visit my brother's home (in Virginia) for her party and Christmas festivities.
I told her she should appreciate me as a good uncle. A lesser uncle would give her one gift and tell her it's for her birthday AND Christmas. I never do that. I always give two gifts.
Buying gifts for her is easy. She loves Lego products and has for years. She tells me the ones she wants to get and I choose one. Simple!