Preferably, as/when contact is made (with an aggressor's striking arm), that contact is made as close to their shoulder as possible. This allows for the tori's hand to (both) motion the arm away from it's intended target, and to slide down the arm towards the wrist/hand (for manipulation purposes).
Keeping this contact in mind, it's important that the tori not "swing" their arms (widely) to either side when initially making these motions. The tori's (deflecting) arm will raise straight up/forward (towards the uke). motioning to either side, is the equivalent to "winding-up" (and serves no purpose).