I suggest from 15-20% of your net pay, and don't touch it.
Now, how and where.. Since the Stock market is so very risky, and the banks are paying a whopping 0.5% on savings, I suggest something different.
US Savings bonds, the EEE's pay some pretty decent rate, I forget it may be 4% or more..
You may diversify in stocks if you wish, just don't put all your eggs into the stock market.. I made a bad move and instead of having 600k in stocks, I now have barely over 100k, bad bad decision on my part.
Main thing is to start NOW and continue, do not remove the funds to buy cars, furniture, pay medical bills etc... savings are to be saved for retirement.. it's easy to listen to the naysayers that "YOU" aren't gonna get old.. don't do it.
If you decide to go stocks for a major portion, I suggest things like Home Depot, Southern Company, Harley Davidson, Wal-Mart etc these are stable companies and seldom have large setbacks.
Examine the stocks p/e ratio [price earnings ratio] it's late and I cannot remember the suggested figure.
Stay away from "Growth" stocks, instead go for ones that pay dividends, always reinvest the dividends.
Also stay away from "commodities" ,, way too unstable to gamble on.. a friend of my Sis' lost almost 1/2 mil on Gold/Silver
Main thing is to put money away and leave it alone.