brace oneself for something
1. Lit. to hang onto something or prop oneself against something in preparation for something that might cause one to fall, blow away, wash away, etc. Hold onto the rail. Brace yourself. Here comes another huge wave.
2. Fig. to prepare for the shock or force of something. Brace yourself for a shock. As the boat leaned to the right, I braced myself for whatever might happen next.