The starting point for any retirement plan is an understanding of what your retirement needs will be. Once you've done that, you'll have a goal to build toward. Defining your retirement needs requires both an estimated retirement age as well as an idea of your retirement spending needs. Your retirement savings plan will follow, driven largely by what you've saved to date and what you can save going forward. Don't forget to factor in any pensions or social security payments you're entitled to receive.
Use this calculator to find out how much you should save for retirement.