Get out a piece of paper.
Write down all your regularly monthly billed expenses and it's cost on a list: rent, car insurance, car bill, cell phone, regular phone, cable, water utility bill, electric utility bill, gas utility bill, gym membership, Netflix, etc.
Write down all your regular non-billed expenses per week: food, gasoline, household stuff, health & beauty stuff, etc. It fluctuates every week probably.
To get an approximate average of your weekly, non-billed expenses: add up four weeks of your expenses and then divide it by 4. Now, multiple that by 52. That's your average expense in a year. Now, divide that by 12. That's your monthly expense.
Add the total of your regularly monthly billed expenses and your average regular, non-billed expenses. This is your total monthly expense. Your net income should be more than this. If not, then you are losing money every month. Otherwise, subtract your total monthly expense from your monthly net income. This is how much you should save into your savings account. It will help to cover unexpected non-billed expenses, like car repair, medical injury/sickness, etc.
If you aren't saving anything, then, you are probably spending too much on non-billed expenses, like eating out at a restaurant or prepared/take-out food too often, drinking at the bar/club too often, going on spur-of-the-moment vacations, going to the movies/entertainment, shopping (clothes, hobbies, whatever non-essential stuff).