Every year, I track biplane's work flow by job orders and dates completed. Based on past records, I can predict within a two week period, which will be my slowest weeks of the year for job orders and/or job completion. As much as possible, I schedule my vacations during these periods, to inconvenience my clients as little as possible. These periods are currently consistent as the last week of May/first week of June and any two week period in December.
I have limited my days working away (consulting, teaching, attending continuing education) from the office as much as possible. Typically, I take all my work files and lap top with me on these trips to assist clients, even while I'm away from my office. I stay in hotels with high-speed internet access, so that I can continue to send proofing correspondence and upload files to printers and publications for printing.
Clients subscribing to my regular email blasts are notified of these working and vacation absences in advance, sometimes more than 6 months in advance. I want to be able to work ahead with them to accomplish any tasks that would need to be completed during these work outages.