Let's keep this short and sweet: the ability to communicate clearly with your clients is probably the most important part of running a business.
You can be the world's best at what you do, but if you can't speak to your clients in a way that they understand and 'click' with, they aren't going to want to work with you.
Clear communication builds trust. It allows your clients to feel confident that you know what you are doing and can actually help them (and if you can't, you'll refer them to someone who can rather than trying to BS your way through it).
Clear communication isn't about being able to rattle off the entire dictionary. Having a big vocabulary might be useful for playing Scrabble, but when communicating with clients, it's better to stick to language you both understand. Explain things in practical, everyday terms, not with a ton of jargon. This isn't dumbing things down. It's communicating in a way that will actually be heard.
Remember, too, that communication is a two-way street. Being able to listen to your clients and hear what problems they are facing is important. Half of communication is listening, after all. If you can listen effectively, you'll be able to respond in a way that is well suited to the situation.
Communication is not just in-person interactions. It starts from the first moment someone learns about your business, whether that is your website, an email, a print ad or social media. Are you communicating clearly what it is that you do and why folks might want to hire you? Those first impressions can go a long way in building strong client relationships, as they'll have a good idea what to expect from you before they ever meet you.
For many of us, communicating effectively is a learned skill. The only way you're going to get better at it is with practice. But it's such an essential part of a running a business, you'd be crazy not to.