You always need to be aware of how much money you need to put on the side because of bills and things that you will need to pay, you also need to save a percentage of what you are earning.
If you manage to do only this and you are managing your money good enough.
The biggest thing is to have a income that can be divided into two parts, one for expenditures and second one for saving, if someone has an income which cannot be enough even for his expenditures then he would probably not be able to save anything, though managing the money while spending is needed but if someone does not have anything extra he would not be able to manage them to save something out if it.