Selling - people buy from people they know, like, trust and value. Learn to sell. In business you're always selling - to your prospects, investors and employees.
Word of mouth - if you could master the most valuable form of marketing, the one that consumers trust above all others, would you instead choose to leave it to chance?
Advertising - if you are not getting attention, it's not working. Make your advertising more powerful, more effective and yield greater results.
Speaking - by becoming a better speaker you can enhance your reputation and open up countless opportunities.
Writing - it's no coincidence that people who write well do well. Writing well is one of the best ways to advance your career and your business.