Absolutely get a decent skincare routine that is within your budget both time and money wise (or you will never stick to it) and that suits your skin.
The difference it makes is remarkable.
Ditto eyebrows. Under normal circumstances I get mine waxed about three/four times a year and keep on top with tweezers in between. Mine are quite dark already so I don't bother tinting them but would recommend it if they are very pale.
Clothes that fit properly. Might involve taking a things to the tailor. Better to buy a bit big and get bits taken in than the 'right' size and have it not fit properly. A £10 primark dress can look like an £80 dress with a good tailor. Wear stuff that makes you feel fabulous whatever that might be. It will absolutely shine through in your demeanour.
No tatty shoes. They don't have to be break the bank expensive, but no scuffs/holes/not dirty.
Take care of nails including cuticles. Doesn't have to mean getting gels and manicures all the time but keep them a reasonable length, clean, shaped and buffed. A bit of cuticle oil goes a long way.
Sunscreen and plenty of it. Skin cancer is not sexy.
Make sure your hair is healthy looking, whatever colour or style you choose. But length rats tails will never look as good as a healthy shiny bob, but a fried and frizzy crop will equally never look as good as long healthy locks.
A good hair dresser should be able to recommend a colour and cut that will bring out the best of your features.
Long term look after teeth.
Try to get as much sleep as you need, rather than as little as you can function on. For me (and my df) that is a minimum of 8 hours, for my dp and dm, it is 6 (lucky sods). For my ds it's 11. Everyone's sleep needs are different. Find yours and meet them.