expect a massive upheaval towards the end of your 40s as your body and spirit readjusts. So love that still young body (you'll love that new older body too), show it off, take pleasure in its strength and agility. (I didn't do this enough). And do stuff with your parents now - as they get old very quickly.
Keep up with IT otherwise at 60 you'll be completely unable to work a computer or whatever we have by then. ( I did this but have friends who didnot and who take forever to do simple tech things).
Learn how to do some basic practical things if you don't already know. Even if your happily living with someone who does the car maintenance, puts up shelves, unblocks the bog and sorts out leaks, one day, they wont be there.
One day, you'll realise you are invisible, so start practising NOW not measuring your worth by how you look.
Buy those shoes - your feet won't want to wear them when you're fifty four (me)
If you have DCs it is amazing when they leave home and you rediscover your own self. You are in there, under the mum costume.
Don't stop reading - or your power of concentration will shrivel to a quick swipe of FB.
Get off FB!