We're well into the second half of the calendar year, and if you haven't already done so, now is the time to do some tax planning. If you wait until you sit down with your tax forms next spring, it will be too late to do much of anything to improve your tax picture.

Opportunities to reduce the number of dollars you pay to Uncle Sam (and probably to your state tax collector as well) are found in many different areas. It's difficult to categorize them, so here are some ideas, presented in no special order, for your consideration.

One of the best tax breaks around is the Individual Retirement Account, or IRA. IRAs are now available to just about everyone who has earned income during the year. If you have taxable earnings from any source, you may deposit up to 100 percent of those earnings, but not more than $2,000 a year, into an IRA.

There are really two kinds of tax savings with an IRA.

First, you may deduct whatever you deposit into the IRA from your taxable income, thus reducing the income subject to tax dollar-for-dollar by the amount deposited.

Second, all earnings by the dollars previously deposited are exempt from tax until you get around to withdrawing the money, presumably after you have retired and are in a lower tax bracket.

This second break is the reason for recommending early action. The sooner you deposit funds into the IRA, the earlier you begin accumulating tax-deferred earnings. Depositing your IRA money early each year can make a difference of thousands of dollars in the final result.

HR-10 accounts (also known as Keogh accounts) are somewhat like IRAs, but are intended only for the self-employed. Limits for 1983 are 15 percent of earnings from self-employment with a ceiling of $15,000. (Starting in 1984, the limit goes to $30,000, and other changes make Keoghs very similar to corporate pension plans.)

If you invest in the stock of qualified gas and electric utility companies, you can exclude from income up to $750 ($1,500 on a joint return) of dividends that you are having the company accumulate for you in the form of additional shares. If you hold the shares for at least 12 months, the receipts on sales will be taxed as a long-term capital gain.

If both spouses work, a married couple can exclude from taxable income 10 percent of the earnings of the lower-paid spouse up to a maximum exclusion of $3,000. If you qualify for this exclusion, you can realize some additional cash now by filing a new W-4 claiming one or more additional deductions.

Parents who are trying to accumulate funds to help pay college expenses for a child may put the money in the child's name and social security number, and earnings on those funds will be taxable to the child rather than to you. They may escape tax altogether or at least be taxed at a much lower rate. A simple custodial account may be adequate, or you may be interested in a Clifford trust or a no-interest demand loan. (See your tax adviser or attorney for an explanation of how these work.)

If you have your investments concentrated in things that generate taxable dollars, such as passbook accounts and certificates of deposit, corporate bonds and stocks or money market funds, you ought to take a look at your present tax bracket.

Your income, and thus your tax bracket, may have changed gradually, and you may now be paying tax at a high enough rate to make tax exclusion attractive. You may want to transfer some of your investment dollars to tax-free municipal bonds, bond funds or unit investment trusts.

Single-premium deferred annuities also offer an opportunity for tax savings. Many annuities are offering pretty high current returns, and the earnings in the account accumulate without tax liability until you withdraw the funds.

Some tax shelters offer substantial tax savings in the form of depreciation deductions or start-up expense write-offs. But study them carefully: any investment, and specifically tax shelters, should be bought primarily for its investment potential rather than for the tax savings it can offer.