Know your audience.
It may sound obvious, but in order to effectively communicate with customers businesses must clearly define their target audiences. Without an identified audience, messaging can be vague, or even worse, it can alienate your customers.
After nailing down your audience, which can change and evolve as your business does too, you can determine how to best connect with them. Do they prefer to get information through Facebook or Twitter? Will a weekly blog be more effective? Do you really need a mobile site? All the answers to these questions will be clear after you have determined who you're targeting.