Hmmmmmm, this is a hard question because either there are different solutions or no solution. Sometimes it helps to just put it away and then come back to it weeks or months later. If it's fic I might try a new round of canon review or just a rewatch/reread to get back into the characters.

I agree that sometimes the hardest part can be to recognize that you have writer's block, especially when you're very busy or tired and the seemingly deliberate procrastination is in truth the dreaded block. It's been a bit of a recurring theme with me lately and what helped there were... deadlines and having to break through the block in time to meet them. To break through what helped was writing a bad draft first and then revisiting it and basically rewriting the whole thing twice.

For me, it's always easier to rewrite something than starting from scratch.