Complete systems training and induction programme. Training how to use a good system takes about one tenth the time it takes to teach people how to do the job.
Document and picture all tasks in an operations manual. What needs to be done, when it needs to be done, who should do it, what the standards are, and how to measure the results.
Say no when you need to. Don't waste your time or that of your clients/customers by entertaining doing work you can't do well - this will add value and credibility (and ease your stress).
Get in the experts. Getting some outside help will free you to do what you do best - no-one can manage everything in running a business. We all have specialised knowledge.