How should I approach managers when turning in applications?

Introduce yourself. Turn in a resume and a cover letter with the application; that will put you head and shoulders above the rest. Ask for their contact info and the best time to get in touch with them, and thank them for their time.

I think you should spend a little time thinking about their organisation/company and when you show up say why you would like to work there in a sentence or two.

Hi my name is Bella. I would like to leave a copy of my resume with you. I very much admire your company because of its excellent customer service reputation/reputation for innovation/ and would value an opportunity to work with you if an opportunity arose. I would prefer a full-time position but if a casual, temporary position comes up, I would definitely be interested.

If you are open to doing some work experience for free – tell them. Turn up dressed well and presentable in case they ask you in for an impromptu interview. First impressions are everything. No spelling errors in your resume etc. Hair neat, shoes clean. Look like you want to impress them and you care what they think.

Be confident and polite. Head up, shoulders back, keep your eyebrows raised, maintain a healthy amount of eye contact. Should it come to handshakes, try to match grip strength, do not try to out-grip.

This in addition to the above.

I agree with @Nullo‘s point that what is not said, matters just as much as what is said. The only thing he did not say that I would add is smile, especially if you are female. His point about handshakes is very important. Women often have weak handshakes, and it is awful. Shake hands with your dad, uncle, someone who can coach you on a good handshake. I am a woman, and I hate shaking hands with women who are incompetent handshakers, and it happens a lot. It probably did not effect if I hired or someone or not in the end, if they were great on every other measure, but it was annoying. You don’t have to offer your hand first to intitiate a handshake, but if they put out their hand, best you be able to do it well.

What type of companies are we talking about? Retail? Consumer Goods? Tech companies?

Go in to the workplace dressed as if you’re going to be interviewed. Walk around a bit and be seen before you do the old standby of turning the app’ over to a reception desk or customer service counter.

Depending on the workplace, a handshake is more important than you think so the above advice is good. Straight posture is good. Smiling warmly is good. Giggling is not so good.

Envision what makes the Chik Fil A and In & Out Burger employees so easy to approach and like.

Bella´s advice is very good. I would add that If you´re at a career fair, you can also practice with companies you´re less infatuated with first (you can do that by studying the fair map and writing down the order you want to visit the booths ahead of time)