brace (oneself) for (something)
To physically or mentally prepare oneself for something, typically something that is imminent, in an attempt to limit any adverse impact. I braced myself for that big bump by holding onto the seat in front of me. I had braced myself for rejection, so hearing that I'd gotten the promotion was a very pleasant surprise!
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.