The art of getting an exit row seat on VS is quite simple - you pay for it!
I always pay for exit rows when I travel in Y - they are narrower that standard Y seats, due to the trays being in the armrest but IMHO the extra leg room more than compensates for this.
Prices vary depending on route, and you now have to be booked in Economy Classic to buy one.
In my experience, they are quite popular, so the sooner you book the better.

Nick