Grantham Video gives excellent advice

if you don't have time to watch it the summary is:

1. equities are historically cheap but not "dirt" cheap
2. investors with a long term horizons (7 years +) can start to buy quality "blue chip" companies now, but should take their time over then next year and one half
3. keep cash on hand-- the more likely you are to freak out when volatility occurs, the higher your cash holdings should be