A good way to measure the performance of your investments is over the long term.
25-30% returns are easy to get! It's not going to be 25-30% in a single year, though. You shouldn't expect more than about 4% real (inflation-adjusted) return per year, on average, over the long term, unless you have reason to believe that you're doing a better job of predicting the market than the intellectual and investment might of Wall Street - which is possible, but hard. (Pro tip: It's actually quite easy to outdo the market at large over the short term just by getting lucky or investing in risky assets in a good year. Earning this sort of return consistently over many years, though, is stupidly hard. Usually you'll wipe out your gains several years into the process, instead.)
The stock market fluctuates like crazy, which is why they tell you not to invest any money you're likely to need sooner than about 5 years out and you switch your portfolio from stocks to bonds as you approach and enter retirement.
The traditional benchmark for comparison, as others have mentioned, is the rate of return (including dividends) from the Standard and Poors 500 Index. These are large stable companies which make up the core of larger United States business. (Most people supplement these with some smaller companies and overseas companies as a part of the portfolio.)