William Bernstein is one of the most respected financial minds of our time. His book, The Intelligent Asset Allocator, should be read by every investor. In an insightful commentary entitled What the Investment Industry Doesn't Want You to Know, Bernstein observes that investors "can only positively impact one aspect of investment performance -- your allocation of assets among broad asset classes." Stock picking, mutual-fund picking and market timing are "irrelevant."
Keep this advice in mind, since it is the primary reason why your 401(k) is probably a "clunker." Here's a checklist of others: