I know I'm a little early on this since I have a few more years until I reach financial independence; however, it doesn't hurt to at least have the ideas floating around beforehand. There's a few school's of thought on early retirement. Some people prefer to have all their expenses covered from investment or other passive income sources while others prefer to have a good chunk of their expenses covered and have the rest covered by part-time work whether at the same job but scaled back or a new one altogether.
I'm in the all expenses covered camp. I like the job that I currently have except for having to be gone from family due to work for a good chunk of the year. There's no way I'll be keeping this job after I reach financial independence; however, I have thought about working at some small businesses near my house as well as teaching whether in the public school system or occasional seminar type classes on personal finance. It's still a few years away so I have time to decide.
Back to the topic at hand, if you choose to have all your expenses covered you need a margin of safety. A margin of safety is how much of difference between meeting the actual value and the minimum requirements. When designing a building, I'd hate to know that each floor was designed to hold 20,000 pounds and no more, when the typical load is 20,000. There's no margin of safety there, you could bring in one extra chair and cause it to fail. The margin of safety I'm after though is the difference between my investment/passive income and my expenses.
A margin of safety is the only real way that you can plan for all the variables that come into play when you're looking at a potential retirement span of 50-60 years. Inflation is unknown; dividend growth is unknown; possible dividend cuts are unknown; medical expenses are unknown; potential emergencies such as a roof leak or a/c breaking as well as many others. So a margin of safety is our way of combating the unknowns.
My total expenses in 2012 came to $20,000 and some change. So at the bare minimum I'd need my dividend income to provide $20,000 annually. As of now my plan is to add another 10% for the margin of safety which is another $2,000. From here I'll add another $3,000 to cover travel expenses because I do expect to be travelling more. So with the margin of safety my required dividend income is $20,000 + $2,000 + $3,000 = $25,000 in 2013 dollars. My plan is to also have at least 1 year of expenses saved up in cash in a savings account; however, that's likely to change depending on the whether we carry a mortgage or not.
Have you thought about how much cushion you want? How much are you aiming for? Are you planning on seeking out part-time work to augment your passive income?