Mark the newel posts in preparation for pre-drilling holes for the railing brackets. Do so by first positioning a pre-drilled bracket against each post. Insert a pencil into the bracket screw holes, and use it as a template to transfer the required hole positions to the face of the post.

Bore holes at your marks with a power drill and a small bit.

Level a bracket on the post, clamp it in position and secure it with rust-resistant screws driven into the pre-drilled holes. Repeat the last three for both of the brackets on each post.