First off, your employer match is essentially free money. It's foolish to ignore that. The tax benefits can also be significant. For instance, I contribute 25% of my pre-tax salary to my 401k. That works out to $1500 a month but because my taxable income is lowered my monthly net is only decreased by about $950. That's $550 a month into savings that I wouldn't have previously had due to taxes.
If you follow the investing philosophy of John C. Bogle, founder of Vanguard, you'll likely do just fine. Assuming you're young, you just split your 401k between four index funds: total bond market, total domestic stock market, total international stock market and real estate investment trusts (REITs). I do 20/45/25/10. Yes, in the short term you might take a big hit but in the long term (>20 years) this is historically shown to perform very well. As you get closer to retirement you increase the proportion of your portfolio in bonds so as to lower your risk.
You don't even have to manage the split yourself, there are plenty of mutual funds that target certain retirement year changes and rebalance the portfolio as appropriate (basically: less risky investments as your retirement date nears). There are fees for this, of course, but for my fund they amount to $90 per 10 years per $10,000 invested. I think that's worth it if you don't want to actively manage your retirement portfolio.