Its summertime and our thoughts turn to things like barbecues, beaches, baseball and investments. Well, maybe not investments. In these uncertain times marked by scary, fast-changing markets, you can't live your investment life by hearing that Wall Street saw to just sell in May and go away. First, make sure you asset allocation is where you want it to be. After all, asset allocation more than the specific funds, stocks and bonds you buy is the most important determinant of your performance. Add up all of your investments, your regular brokerage accounts, your IRAs, 401(k) plans, certificates of deposits and so on. Figure out how much you have in stocks, in bonds and in cash to have investments, and see if those percentages are aligned with your time horizon and your tolerance for risk and volatility.On a related front, have you rebalanced your portfolio lately? You should rebalance at least twice a year. If you run a twice a year schedule, the middle of the summer is as good a time as any to take steps to make sure things havent gotten out of whack. You may be sitting on a lot cash. Many cash-type have investments, particularly treasure bills and money market funds are paying next to nothing. Shop around, particularly at banks and credit unions for better yields for your cash. Finally, this is a good time to check your costs. Costs are one of the few things investors can control. Are you paying too much for brokerage commissions? Plenty of online brokers charge us a few dollars to trade stocks. Are your mutual funds charging too much? Consider switching the funds with lower annual expense ratios. If youre sitting on losses instead of a regular account, realizing losses will also allow you to lower your 2009 taxes. And with the money you saved on taxes, you can afford a better vacation. I'm heading for the beach.