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A firm handshake

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Confidence

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Presentable appearance, clothing and hairstyle - no shaven heads or curly locks, and especially no earrings.

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Clean vehicle

It's a fact that jobs have been offered just on a person's appearance. I know, because it happened to me, and no-one even asked to look at my logbook or licences.
However, in the normal course of events, for low-timers, and anyone else for that matter, visiting as many companies as possible is about the only way to get yourself known. Just sending a resume (see below) is not good enough when they haven’t seen you before

Believe it or not, someone with relatively low experience and who gets on with customers is actually in a better position than somebody the other way round, other things being equal, as experience and flying techniques can be taught – personality can’t. Also, get to know lots of people at the bottom levels, because Chief Pilots very often ask the guys on the shop floor if they know anyone when there’s a vacancy and, if you are recommended, there’s less chance of personality conflicts later (Chief Pilots don’t like hassle, but they do like people who are not going to drop them in it, as they carry a lot of responsibility). At least one company of my acquaintance gets all the pilots in the crew room whenever a potential employee is about to be offered a job, and they vote on their acceptance.
Remember also that loyalty goes both ways. Some companies deserve all they get when their pilots disappear in a shortage – with no staff, they can’t trade, and they go out of business. It’s happened before and will happen again. On that basis, if you’re doing the traditional two years as a hangar rat before you get your hands on a machine, be prepared to move on if it seems like the company are more interested in your cheap labour than training you. In my opinion, in with your normal windscreen-washing, you should be doing the air tests and non-revenue flying, which will not only give you an incentive, but make your subsequent training cheaper by keeping you current. It is entirely possible to get well upwards of 400 free hours a year in a busy company, if you’re prepared to end up in strange places for days at a time.