Guide ti income tax preperation. CHRIS USHER/SENTINEL BOX: What other tax moves you should consider Only one Internal Revenue Service deadline has already passed this year - the final payment of 1988 quarterly estimated taxes to cover self-employment and investment was due Jan. 17. However, there are several tasks that you should complete right away if you haven't already: - Start your 1989 record keeping by setting up separate logs for your business travel, entertainment and auto expenses. If you plan to contribute to an individual retirement account this year, act soon to get a year's worth of tax-deferred compounding. - Estimate the amount of money you have in your tax-deferred retirement savings plans. If it exceeds $500,000 or so, make an appointment now to meet with a tax adviser. Your last chance to shield your nest egg from 15 percent excise taxes on any excess distribution when you retire, regardless of when that is, ends when you mail in your 1988 return. Deciding which of two key elections to make on your return requires lengthy, complex calculations. - Shop for a 1989 tax guide. Even if you do not prepare your own return, a guide will help you organize your records. - Consumer interest is only 20 percent deductible this year. Starting with your first payment in 1989, set up a schedule to pay off your credit-card balances and other personal debts as soon as possible.