How much do you make?
What are your regular monthly expenses (housing, food, utilities, car, etc.)?
What are your average expenses for other things (entertainment, vacations, gifts, etc?
Consider using a personal finance program to track your income and spending. Mint is free and secure, but it does have advertising. 
 

Start with your fixed expenses and needs.
Pay yourself first! 
What else would you like to do?  Put aside enough money to cover these expenses -- when you have accumulated enough, give yourself permission to enjoy yourself.
Use credit wisely -- for long-term investments, not for day-to-day expenses.

Put some money aside for repairs, maintenance, health care and similar expenses you can expect to incur.
Consider life and disability insurance to protect your capacity to earn money.
Have health and property insurance to protect your assets against loss from unlikely, but potentially catastrophic expenses

It's never too soon to start thinking about the long-term.
Go for the big picture -- children's education, family, retirement
Use the Actuary's Longevity Illustrator to understand how long you might have to plan for -- it is probably longer than you think!
Balance how much you can save and how long you'll be able to work with your desired lifestyle in retirement.