I get a paper and a pen and write down what I know I have to do, what I don't know how to do it and I suspect I don't know yet what I'll have to do.

For the parts I know I'll have to work using a new framework or new tools I try to create a proof of concept project I can reuse later.

I tend to write a bit in paper before coding just to wrap up my head on what I'll have to do.