Haven't been trading for too long - about two years now, full-time, but the most important thing I have learned is MANAGING CLIENT'S EXPECTATIONS. I have dealt with two particularly difficult clients out of about 30. Dealing with one at the moment who, after watching the DVD they sent forward a two-page list of changes even though my contract specifically forbids creative amendments. They absolutely went GA-GA over their ten-minute highlight reel which I posted on-line, thanking me and telling me how blown away they were - so I am confident I have the creative and technical ability, but when it came to the full-length DVD, there's a list of things like "why haven't you made our home look more beautiful" (even though going to their home that morning to film their preparations was a freebie extra) and "there's a centimetre cut off the top of my head during the speeches, very unprofessional" and "more of the singing!" and "more of the hotel grounds! why isn't there more of the hotel grounds!"
So, here I go again, updating my contract. My most major flaw since being in business is not managing my client's expectations. I must be explicit about what they are going to receive. My wedding DVDs are around an hour and 40 minutes, but I truly believe that some clients think that 10 hours of attendance means 10 hours of filming.
You live and learn, I suppose.