Mix it well, let it settle a little - its a bit like using washes, the effect can vary if used immediately or after 5mins. (let the heavy stuff drop)
Thin it down - water or medium based stuff.
Brush on but dont leave any area with a flood of it. Not too wet.
Leave it to dry before the next coat if any.
If you have an empty pot of the same volume, transfer 50% over, add the right thinning medium (acrylic makers do have thinners available) and mix to both pots.
I use spray as I sometimes use Tamiya weathering. I put some on under the matt, then add a top coat over, sometimes fast as it stays stuck.