This is a quick, but very effective tip I think.
Sometimes you’re writing along, and it’s all flowing very nicely indeed. Then you get to a line which you just can’t compose. So you sit there, staring at the annoying blinking cursor, and soon your flow dissipates and you’re stuck. Much coffee is imbibed, and pretty soon bad TV hollers its alluring siren call.
I’ve found that the best way to stop this is to not write the offending line. The moment it feels like I’m about to get bogged down, I type JOKE, or LINE, or WORD, and carry on. By the time I come back to it, my brain has often resolved the quandary; and I’ve written three extra pages in the meantime.