the increments usually depends on how much narrow is your grip before the add, amd how much wider you use the grip after the add.
I found that add 1.5-2 kg when the grip is at 15cm+ shoulders distance, let me work with a medium grip not to more.
At the beginning you can find that lift the weigth is too difficult but ,as the IM is for the most traps work + extra rotational movement around the shoulder joint, you can grab the bar with firm grip and think before to start the lift to pull the hands in opposite directions over the bar. this stimuli activate some motors pattern in your premotor cortex. in that way all the muscles you need to perform the movement are activated at the same time. every time your bar is soming down in the front think about this pull movement and you will able to slow it down.
