[Lambdanaut]

Really it's just a lot of googling and looking for good tutorials that explain how the Bitcoin protocol works. Whenever you hit a concept you don't understand, google it.

The Bitcoin Developer Documentation is gold: https://bitcoin.org/en/developer-documentation

Start by defining your basic objects, and then begin adding their methods, just like you would any sort of program. The basic objects here are the Blockchain, Transactions, and a Client to interact with the chain. The rest is just implementing rules for how these objects work together.