If your partner tries to move to the side or up or down shift your elbow so that it stays in line with your partners elbow. This involves a slight twist of the wrist. With practice this can be done as soon as Nage tries to initiate the movement. There is no noticeable movement but Nage feels like the trapped hand is stuck in a hole in a wall and any movement is impossible. To begin learning it is good and probably necessary to make large movements so that your body can understand the forces.
If Nage pushes Uke drops the elbow slightly so that it is below Nage's hand. This causes an upward force lifting Nage's center and making it very difficult for Nage to move. This usually involves a slight twist of the wrist.
If Nage pulls Uke slightly raises Uke's elbow. This helps center Uke making Nage's pull much less effective.
If Nage tries to break away by bringing Nage's hand back like Furi kaburu then I do not know how to keep the hand immobile. It is easy for Uke to push into Nage's elbow and shoulder. Taking nage's arm to the Up position. A slight twist is required. From this position Nage is off-balance and Up techniques are available.