Like you, I was total skank monster when had DS1. So, determined to look much better after DS2 here is what I did:
Cut & colour week before due date
Ditto leg and eyebrow wax (have eyebrows like werewolf so once waxed would maintain daily/every other day to keep looking lovely)
Treated myself to a few pairs of nice pjs and dressing gown so that I could feel nice even when slobbing out
Whenever I had a spare moment I would do something for myself - quick file of nails, slap on moisturiser on feet/hands/face. Better still, train toddler to give mummy a foot massage with nice cream whilst you feed new arrival
Pared down beauty routine to bare minimum of tinted moisturiser, mascara, blusher & lippy - 5 mins max to apply.
As soon as I could fit into normal clothes, I treated myself to a mini shopping spree at Hennes to give myself a few nice but cheap outfits to tide me over until I could get back into my regular stuff.
Only ever take black & white photos during birth, labour and post-natally for at least the first two weeks! B&W hides a multitude of sins and makes your skin look fresh and dewy even when its not
Make sure you get quick shower before DH/DP leaves in the morning. You may not feel like getting out of bed just then but you will feel better for having done it with someone else overseeing kids rather than you trying to amuse both of them through the shower screen
Most importantly.....accept you will have your crappy days where you cannot get a second to yourself, can't get dressed until 2pm, no shower and your hair resembles a birds nest. Learn to shrug it off and enjoy your slob day