I've been at this for 2 months, so still a beginner. Most important lesson I learned: "Plan your cook, and Cook your plan". The biggest adjustment for me was timing. I was used to grilling something for 20 minutes, and didn't need a lot of advanced planning or time from grill to table. With my first few SV cooks, I always found myself rushing to finish by serving time (especially if starting with a frozen item). Now, with SV, I work backwards to be sure I start in time.
I want to cook a steak for 2 hours and serve at 6pm. I DON'T setup and start my APC at 4pm. Big Duh! There are lots of other steps: 15 minutes to bring water to temp, 15 mins at the end for searing and final prep. So, I need to get started no later than 3:30, and be sure the meat is thawed at that time!! This is a lot earlier in the day than grilling. SV doesn't take more time, it just takes a different schedule. Once the water is up to temp and food is in, there's not much work until sear and serve time. Now it's part of my routine, but definitely took a mental adjustment -- especially on days when we eat a SV dinner at noon. I start cooking dinner before I eat breakfast.
Second big lesson is warming serving and dining plates, especially for low temp cooks (like med-rare steaks).