A dark colored, well tailored blazer
You can spend $200 or $2000 on a blazer but if it doesn't fit properly you'll look like a buck fifty.
The man 5'9" and under should go for the short. Your blazer shouldn't look like a tunic.
Although sized according to chest, the blazer should fit properly in the shoulders. If you can see your deltoids it's too small.
The old adage is, if a man wants one jacket in his lifetime make it a dark blue blazer.
A good haircut
Find a stylist that knows you and your style. My husband pays more for a haircut than I do. His justification is that if he went to another stylist he'd look like a cheap used car salesman with a comb over. Seeing as your partner should complement you when you're out together I'm willing to hold off on a pedi to keep him looking and feeling sexy. You may not notice it but glances go straight from your face right to your shoes. Which brings us to our next point:
The finest quality shoes
Your shoes should be the most expensive, highly crafted piece you're wearing. Good shoes can make an inexpensive outfit look like a million bucks. Black wing tips like those by Salvatore Ferragamo, Tom Ford or Ermenegildo Zegna are safe and timeless.
A classic watch
The wrist is an area for chic understatement. Don't be too aggressive or too skimpy. Some recommend building your watch collection to mix with your wardrobe. To start, go for a classic in steel, silver or white gold like a vintage Rolex Oyster Perpetual, Van Cleef & Arpels Latérale or a classic Timex Mercury.
Proper pants (including denim)
By 'proper' I mean those that suit your body type. Not everyone can wear skinny jeans or drain pipe trousers. If you're tall, stay away from pinstripes. If you're short, choose pants in dark fabrics. Most importantly make sure your pants are hemmed properly: Pant Hems - What You Need to Know
10 Fashion Mistakes and How to Avoid Them
Pant Hems: What You Need to Know
How to Tie a Skinny Tie