Start here. I'm serious.
This and Cryptography (Encryption, Hashing Algorithms) is another hugeeeeeee factor to consider.
On top of that, start with getting some knowledge on distributed networks and economics.
Once you have knowledge in the required domains, ideas will automatically start falling into place and you will automatically start doing research, read papers written on cryptocurrencies, improve upon your own ideas, grab new ideas from others and bamm! You're an expert
But seriously, its not as easy as it sounds. XD
Now that I think about it, theres a lot of stuff to think about to create a cryptocurrency. XD