Just wanted to post this for others to benefit. Be warned: it's a bit wacky. But it's worked for me every time.

Find a quiet area. Act out the last scene you had concretely planned.

I know how it sounds, but get into it. Get animated! Feel your character's voice. Commit to their actions, with props if you have to! If you really explore their minds from the inside out, you'll say or do something naturally that they would do next. It will give you a good place to build from. No lie, I do this in my basement when I'm really stuck. Some of my best-written scenes were acted out in that cold, dank basement.

Happy writing all!