2012 before you decide, make sure that its nothing to do with midlife crisis.Then :
1.Have savings which can cover 6 monthly expenses rent, food, fare/fuel loan repayment if any.
2.Agree with your partner before quitting to seek her /his support.
3.Be sure to readjust your living conditions like say moving to a cheaper house as you look for another income generating activity.
4.Make sure that the income generating activity is up and running for about 3 months before quiting.
5.If its looking for another job , first secure the job then quit the current one.If its business refer to point number 4.
punda amecheka