I'll be honest it's hard. Selfishly it's something I admit struggling with as I look at myself and don't see myself if that makes sense.
I managed to get my hair done (for a few hours) with baby, even fed him during. I felt this was a Mumming at its best!
This probably sounds daft but my baby sleeps when in his pram but isn't the best at napping at home, so I actually find it easier to get a blow dry than wash and style my own hair. Dry shampoo and a big clip are essentials for me. If you've got long hair a high pony with a piece of hair wrapped around the tie always looks a bit more done.
I hate having chipped nails, so I've been just filing and putting a clear varnish on which makes them look not too bad. So I'd advise that.
I second the sheet masks garnier do one for tired skin that feels lovely and can be popped on when feeding.
Get your brows done before you have baby as you won't want anyone faffing with you for a good few weeks after.
I bought some really nice loungewear before having baby mostly from Next this made me feel a bit nicer as you are round the house a lot at first, and don't really want to get properly dressed for visitors. And if breastfeeding need really easy access to start as you're getting used to it. I'd really advise this, it really made me feel not too drab and awful.
Lip balm, and eye drops. Tired/dry eye ones for the start and brightening eye drops optrex do blue ones that get rid of redness. A good moisturising lip balm.