For me, testimonials are an important part of getting new business for anyone looking for work. For myself, I make it a priority to casually ask for a referral after each project is complete. I typically ask for two to three sentences directly about how the project went, what the client thinks about my communication and execution on the project. Clients are typically very willing to write a few lines about their experience with you to help out.
Testimonials help to establish credibility for your business and let people know you're the real deal. There are few things more valuable than a great review from a happy client on a recent project. This provides a higher level of comfort for prospects looking to hire you and makes the sales process much smoother when it's time to provide references. Testimonials tell your prospects that other people had a great experience working with you and that you come highly recommended.
I usually give my clients a couple weeks after a project to ask for the testimonial. This gives them time to think about how the project went. I usually send a quick email following up on the project asking if they would be willing to write a quick review. I always tell them it may be published on my website and will include a link back to their site if they wish. I've found clients enjoy giving back in this way and gives them a sense they're helping improve my business beyond the project we just completed.
You can also offer an incentive like a discount on another project or service for writing the testimonial.
I've seen this done several different ways but there are a few common elements that most have. The quote of course, the author, and a link back to their website. Clients love the link back since it drives traffic back to their site and highlights their business.
If you can get good portraits of each of your clients, it's nice to have a small picture of your clients next to their testimonials. This helps to personalize the testimonial even more and shows the strength of the relationship. If you do it for one though, try to do it for all to keep your page design consistent.
Once your client gives you your testimonial make sure to say thanks somehow. In the past I've sent thank you cards, given discounts and even sent small gift cards to say thank you. This says that you appreciate their help and look forward to helping them on their next project. It's the perfect way to end a project with good chances you'll work together again.
If you haven't started collecting testimonials, I would recommend starting now and finding a way to show them off on your website. Let your website do all the heavy lifting when it comes to generating new business leads. When a prospect reaches out to you they should already feel comfortable that you know what you're doing and will be a good choice for them.