I like to take on a mindset of these three concepts: Expectations, Transparency, and Overdelivering.
Setting expectations with your clients means clearly describing the normal course of doing business with you. What does your processes look like? Timeframes? What is inside and outside of scope? What is expected of your client? What will delay delivery of a successful outcome? Communicating expectations allows you to exceed expectations.
Transparency is being open and honest with processes, pricing, and the limits of your services. Communicate often. Own up to mistakes immediately and address them. Be open about potential conflicts or differences of opinion with your client. They will thank you for your honesty and will likely be happy to find a win-win solution.
Overdelivering is another key that will set you apart. Again, clearly communicate outcomes, and don’t over promise, even if you have the best intensions. Always provide something extra: Beat a deadline, provide extra copywriting or images. Add an extra set of revisions.
It might be expensive or time consuming to prevent an unexpected problem. But if you wait for a problem to happen, the costs are dramatically higher, and could even cost you a customer. Use these concepts and add them to your strategy. This will compliment what @christyprice recommends: automate processes, and remove yourself as a bottleneck.