When I will begin to write I try to get some of the general idea in my head first then write it down. Or look up info online if it involves some elements of real things. Always if getting stuck or tried I take breaks then come back to it. Or if taking a break write some side note to where I left off or what I was thinking next to put. Listening to music and actually watching movies help me get my imagination going.
I don't really write fanfics mostly my own short stories or poems.