Various forms are required for preparation of the 1990 tax return, and data from several sources are required to put these forms together. Don't wait until the last minute to start collecting tax forms and information regarding:

Interest expense: Sort records of interest payments into categories such as home-mortgage interest, personal interest, passive-activity interest, investment interest and business interest. Pay attention to the various interest deduction limits -- home-mortgage interest, investment interest and consumer interest. Be prepared to prove to the Internal Revenue Service how you spent borrowed money -- this determines how the interest payment will be classified. Pick up IRS Form 8598 for home-mortgage interest and Form 8582 for passive-activity losses.

Rental losses: If you own rental property and actively manage it, you can deduct up to $25,000 of losses annually against your salary and other income, but only if your adjusted gross income is less than $100,000. This deduction is phased out for taxpayers whose AGI is between $100,000 and $150,000. It is not available for taxpayers whose AGI is more than $150,000. If you had a rental loss in 1990, you'll have to obtain the following IRS forms: Schedule E of Form 1040 and Form 8582 for passive activity losses.

Nondeductible IRA contributions: If you made or decide to make excess nondeductible contributions to your 1990 IRA, you'll need Form 8606.

Children with investment income: If you have children under age 14 with more than $1,000 of investment income, you'll need Form 8615.

Taxpayers who throw their returns together at the last minute invariably end up paying the IRS more tax than they should. If you really want to save taxes, start now. Give yourself plenty of time -- two full months -- to prepare your return. Don't miss any of these tax-savings options or opportunities:

Keoghs: Make the maximum tax-deductible contribution to your Keogh plan if you are self-employed either full-time or part-time. Deductible Keogh contributions for 1990 can be made after the end of the year -- provided the Keogh was opened by Dec. 31, 1990. If you met that deadline, you have until the due date of your return to make your full Keogh contribution.

IRAs: You can contribute to your 1990 IRA until April 15, 1991. But the contribution will not be deductible if you or your spouse is covered by a company pension plan and your adjusted gross income is above $50,000 -- or $35,000 for unmarried taxpayers.

Married-joint vs. separate returns: Most married couples are better off filing a joint return. But some couples, particularly those in which both have substantial incomes, will pay less tax if they file separate returns.

Head-of-household filing status: You may qualify if you are single, widowed, separated or divorced and maintained a household that was the principal residence of a child or dependent relative for more than half the year. Head-of-household tax rates are lower than individual tax rates.

Expense vs. depreciation of business equipment: You can write off, in the year of purchase -- rather than depreciation over a number of years -- up to $10,000 of business equipment or property.

If you expense it, you can get the deduction immediately; if you depreciate it, the deduction will be spread over a period of years. You do not need to have used the property for the full year to expense it.

For example, if you bought business equipment at the end of December and used it exclusively for business for only a few days, you can still take the full $10,000 expense deduction.

Depreciation election: Business assets may be depreciated under an accelerated write-off method, which generally produces large deductions in early years and smaller deductions later on, or under the straight-line method, which produces the same deduction each year. For some taxpayers, the accelerated depreciation may be subject to the alternative minimum tax. Before making the election, it is a good idea to consult with a professional tax adviser.