Start with the basics.
I am 50s but have no wrinkles- used SPF 25+ every single day for over 25 years so if you don't now- start!
If you can afford it, think about some subtle fillers or Botox.
If you have pigmentation on your skin then use some products which lighten it.
Book a make over as suggested- Bobbi Brown, MAC, Estee Lauder, Laura Mercier.
Think about your hair- get rid of anything mumsy or too 'manly' granny-ish.
Teeth- if they are yellow or stained then get whitened.
Stop thinking you need to dress differently now you are 50! I'm no slave to fashion at all and have very few clothes. I buy skinny/ slim jeans, smart cigarette style trousers, knitted dresses and tunics, but rarely anything patterned or flouncy, lots of ankle boots and a few pairs of knee high biker type boots. Maybe this is a boring 50s 'uniform'! I don't go near any shops that are aimed at women 'our' age.
I like nice scarves, simple slightly 'chunky' jewellery in silver or white gold, and basically a 'less is more' approach.
I always wear drop-style earrings in silver or silver & pearl (Claudia Bradby do some nice stuff) or simple diamond studs.