The young woman, her face beaming in nervous anticipation of the job interview, quickly smoothed a slight rumple in her suit. Satisfied she made a neat and businesslike appearance, she stepped briskly into her potential employer's office and knocked over a potted plant.

In a situation where first impressions mean a lot, that's a job-hunter's nightmare, with dreams of the job as shattered as the porcelain pot at your feet.

In this case, however, the interviewer was understanding. Accidents happen. She paid little attention to it.

But many job-hunters do make poor first impressions -- and don't get hired -- generally because of something they easily could have avoided.

Because this is the time of year when many high school and college seniors begin to line up post-graduation jobs, several executives were asked what they look for in a job applicant. They also came up with their list of "don'ts," aimed primarily at neophyte job hunters.

About an engineering graduate who showed up for a professional job interview in dungarees, Teresa Walker, personnel manager for American Communications Corporation of Annandale, said simply: "That does not impress. That's not acceptable dress."

Harley G. McKinnie, personnel supervisor for the American Trucking Associations, Inc., ranks at the top of her personal pet peeves "the applicant for a secretarial position who does not want to type. We don't have," he says, "an elf to delegate the typing to."

Sometimes an applicant will answer a secretarial want-ad but make it clear he or she "feels it is demeaning," and what they really want is a toe in the door for a career postion. "That doesn't work here," she says, "there's not that much turnover."

Don't show up for the interview with a crowd of classmates or friends, advises Linda Lehner, personnel manager for Woodward & Lothrop. "We get hordes who come in together. You should have the initiative to apply on your own."

Job interviews, agree these experts, can be very stressful on the applicants who may feel their whole future rests on the 45 minutes or so they spend in the interviewer's office. Jim Dunn, personnel director for Tel Com, a communications firm at Tyson's Corner, says he may put an applicant at ease by "pumping his ego, telling him he's well qualified -- even the ones we end up turning down.

"You almost feel an obligation for the first-time job hunters. They need all the help they can get."

Generally, say these Washington-area interviewers, they are looking for people who -- assuming they meet the basic job qualifications -- are neat in appearance, show an interest in the company they are applying to and display a sense of self-confidence.

Nobody has to look like "models and beauty queens," says Helga Tarver, head of Tele Sec, whose firm screens more than 100 applicants for temporary office jobs a week. Just "neat and businesslike."

Ann Page, whose Reston Professional Services counsels job applicants on how to handle interviews, believes one of the most important things is to "know something about the company" you're applying to. "Do your homework."

Applicants score low points with Walker if they are "sheepish, too quiet or fiddle with their hands." She prefers an applicant have "an air of being secure and confident. You're always impressed with a 22-year-old who feels comfortable in an interview and can make it a learning exercise."

Tele Sec's Tarver likes to get the applicant to do the talking the first 20 minutes of the interview.What she wants to learn is "if that person is quick and alert, if that person is sincere. Do they stick to business?"

She places a great deal of emphasis on the sense of responsibility the job-seeker conveys and the kind of interest they show in questions about her company and the job. "If somebody asks no questions at all, that applicant is viewed less favorably."

A promising applicant usually gets a second interview, says Tarver. Her tactic then is to find out "how much of that information from the first interview they retained." She suggests the job-hunter take notes. "Very few do, not 1 in 20."

The experts offer these additional tips:

Have a good resume. You may want to write two or three different ones, aiming each at a different kind of job you might want.

Be prepared. Have such basics as past dates of employment. "A lot of people come in not able to remember where they worked and when," says Woodies' Lehner.

Expect to answer such questions as why you left your previous job. If it's because of a conflict with the boss, be honest. "We realize you may not have gotten along in your old job, and for good reasons."

Project a positive attitude. "That's half the battle."

Know what you're after. Instead of "I'll do anything," tell the interviewer "I'm interested in sales because . . ."

Make eye contact.

Even for the determined job-hunter, two interviews a day may be the limit. "Everybody gets burnt out," says McKinnie. "You get tired of selling yourself over and over." She suggests you take a day off and go to a movie "and don't feel guilty."