Denim is casual, formal, essential and for many, regular office wear. It pairs remarkably well with a blazer and T-shirt or shirt. As styles go, a tapered model is the preferred option. Try to avoid washing it if at all possible to retain the colour. Instead, brush out dirt and zip-lock bag it in the freezer every few weeks to get rid of bacteria. Or get it dry-cleaned. A good pair of denim can last decades.