Prepping a floor for liquid DPM

This is the first time I've done this and have a bunch of the Wickes bitumen DPM on order for tomorrow. As I understand it, this stuff should go on like paint? As in, brush and roller, not pouring direct to floor and spreading?

If anyone has done this (or does it for a living), any tips to do it right, bar vacuuming the surface? If there are major gaps behind the skirting that need filling, do you have suggestions as to the best product for this?