Hi! welcome to the forum.
for a start, take a look through Matt Allinson's basics series of articles:
Men's Fashion Basics - Fashion Advice For Beginners By Fashionbeans.com
These will give you a good idea of what kinds of things you should be considering for your wardrobe. It might also be worth checking out my articles on Reinventing your style:
Reinventing Your Personal Style: Refining Your Clothing | Fashionbeans.com
Reinventing Your Style: Refining Your Clothing (Part 2) | Fashionbeans.com
These are designed for the man with a slightly less confident approach to their wardrobe and is essentially about refining what you already know.
The best advice anyone can give is to get the basics right. Have a solid wardrobe of versatile, classic pieces; think jeans, chinos, shirts, plain tees, knitwear and footwear. Get your style right back to its roots and rebuild it from the ground up, make sure you are comfortable in what you are wearing and don't push the boundaries too far. A lack of confidence in what you are wearing is a real killer.