What advice would you give your "first year in practice" self?

I'm about to set up in practice on my own having been an employee in practice for many years.

I know there will be a lot of learning "on the job" but I was wondering if members had any tips to help me hit the ground running. Paraphrasing all those "letters to your 16 year old self type" books, what advice would you give yourself in your first year in practice?

Thanks in advance!