I like the general rule of thumb of saving 10% of your gross income or 15% if you can while still living within your remaining income. This can usually be reached by maxing out your 401(k) contribution that has any type of employer match and then maxing out the $5,000 contribution limit for an IRA or Roth IRA.
Knowing how much you will need during retirement is difficult to determine. A few websites out there try to provide help with the estimate with the purpose of helping you determine the amount you need to save to have enough in retirement. I like to also look at it the other way around; if I save a certain amount now, how much will I have when I retire at a certain age.
Take a look at some of these calculators below and play around with the numbers to see if you are saving enough.