Braced, prepared, or ready to do something in the immediate future. We were all poised to work long hours to finish the project in time for the holidays. The cobra reared its head up with its hood flared out, so I knew it was poised to strike.

"be poised to do" is a correct and usable phrase in written English. You can use it to indicate that someone is ready and prepared to do something. For example, "He was poised to jump off the diving board and into the pool."