There is no secret - it is jsut organisation and prioritisation. I am not naturally soignee, but a frew things that make a difference:
Dedicate a couple of hours or so every week to deep condition hair, use a decent face mask and tidy, shape and polish nails.
Moisturise your whole body every day.
Get a good skincare routine - do it daily.
Invest in good tweezers and a decent magnifying mirror.
Find a good anti frizz serum.
If you wear make up, develop an easy to use and maintain light day time look. Primer is your friend. Take a make up bag with you if you are out for the day.
Foundation garments matter as they help you stay less sweaty, avoid any see through clothes disasters and make your clothes hang better - I always wear a little cami top under my clothes - M&S cotton in winter and Uniqlo airism in summer.
Smart ish dresses in decent quality stretch fabric (eg heavy jersey) and a single bold colour (navy, red, deep pink, dark green etc..) are good for work, as a dress always looks smart and they don't crumple as much.
Black is never a smart or sophisticated as you think it is and if cheap or badly maintained can be very unforgiving.
Deal wth any clothes issues immediately - loose threads, missing buttons, stains, small holes.
Polish your shoes and keep them in good condition. also make sure your shoes work with your outfit.
Find a good scent and wear it every day - carry a small version with you.
Wear decent, discreet jewellery - ear studs and a nice chain necklace.
Carry a spare pair of tights in your bag.
Where possible buy clothes in natural fibres - they just hang better and look more expensive - get used to using the iron (spray starch is your friend).
Don't get hung up on clothes sizes - if you usually take a size 14 but a 16 fits better - get that 16.