The best time to prepare for a financial emergency, of course, is well in advance. If you wait until your car dies, or your roof springs a leak, or your air conditioning unit fails in the middle of August...you could find yourself scrambling to be able to find the needed funds.
You'll want to start making a list of all of your expenses - rent or mortgage, car payment, insurance, utilities, grocery bill, cable, gym membership, transportation costs including gasoline or bus fare. If you find ,even this, too daunting a task, you can simply multiply your present monthly take home pay times six. That number is your minimum money cushion.