1] You are doing the most important thing which is spending less than you make and then investing your savings.
2] Costs matter. Minimize your investment costs where possible. Vanguard (
www.vanguard.com) and Fidelity Spartan Funds both are well managed with bare bones cost.
3] There is a relationship between risk and return. You can buy high grade bonds with minimal risks of losing your principle in the long run, but with a minimal return. Stocks have a much higher month-to-month and year-to-year gyration - but provide higher average returns. Going low risk on everything minimizes returns.
4] Diversify. A well diversified stock portfolio (like owing a mutual fund covering the Russell 2000 or the S&P 500) both lowers risk and raises returns for that category of assets.
What I do is save a lot and have a diversified portfolio (broad stock index funds: both international and domestic; bond funds; liquid assets) and all are at lowest management fees. I use Vanguard and Fidelity Spartan. Then I don't worry about it. During the current downturn I've probably had paper losses of $100,000+. But my time horizon is still 10 years out to start drawing down the money.
Another option is a "target retirement date" fund from Vanguard or Fidelity that gradually shifts your assets more to safer (but lower average return) assets as you get older.