Only when you are the consumers of your own products, can you design the best ones! Same philosophies go for API design and programming in general. This advice may seem counter-intuitive at first, but trust me, the best way to get better at backend programming is to spend some time doing frontend! It will teach you a lot about how your APIs are being used in the "real world". A first-hand experience of API consumption will tell you a lot about your design philosophies!
Me, Mine and Myself