Clinical Experience

Working a clinical job or volunteering in a clinical setting (e.g. hospital, hospice care, free clinic) provides valuable insight into what it means to take care of a patient. Getting clinical experience shows you know how to interact with patients and that you would be capable of being compassionate towards them as a physician. You should have enough clinical experience to write meaningfully about it in your application personal statement and speak intelligently in an interview.

Clinical Employment

This covers what the job typically expects. This can be very different depending on the hospital and region, e.g. rural vs. urban can be different as night and day.

Remember to ultimately do the job you’re most interested in. If you end up in a job you don’t have a passion for, you might hate yourself and even lose interest in medicine. Someone truly interested in phlebotomy will get way more from the experience than an EMT that hates their job.

Scribe

Typically for surgical or ED fields, though other fields are starting to become more available in private practices.
Entirely patient contact but usually no interaction with them, but high clinical exposure. Best educational experience, especially in the ED. You follow the physician and see almost everything they do. You learn how to be a good (or bad) physician. You learn many technical terms. Moreover, you see what the life of seeing patients is truly like.
Learn to write perfect notes, which is helpful in med school.
Job availability depends on location.
Hours are flexible, and some jobs involve a lot of downtime.
No certification required.
Low pay
There are multiple national companies that employ scribes (ScribeAmerica, Elite Scribes, etc.) and a lot of private practices/hospital groups that directly employ scribes. Check craigslist.

Medical Assistant (MA)

Depends highly on the job description. Some MA’s may not work with physicians. The clinical experience can vary from one of the best (involving giving shots, drawing blood, and introducing cases to physicians), to almost all paperwork.
Can be the best for administrative work with the physician. You work as a team member. You learn a lot about the behind-the-scenes work with billing, insurance, and so on.
May not require certification. Even so, an EMT or phlebotomy certification should suffice. Don’t do MA school.
Typical full-time hours. Higher pay.

Emergency Medical Technician-Basic (EMT-B)

Arguably the best clinical experience with a semester of certification. You directly take care of patients by providing inital assessments, airway/breathing/circulation management, CPR/AED administration, and administration of a limited number of medications.
Low job availability and flexibility, especially if you’re not full-time for more than most of the year. Still involves occasional dirty work (e.g. vomit, poop).
Almost always requires an EMT-B certification, which may be a 3 to 6 month course depending on the program. Courses vary in price, with some costing $800 and others multiple thousands of dollars.
You might see seriously messed up stuff. The kind no one needs to see.
Additional resources can be found on /r/NewToEMS

EMT on an ambulance

You and your partner assume total patient care, with little supervision.
Best for patient assessment skills. You ask the first questions the patient hears, with the downside of often not knowing what happens to them, since they disappear into the hospital.
Depends highly on the area you are servicing. E.g. a rural area may see one serious call in a week.
Lots of transporting patients and dealing with drunk or old people. You lift (bariatric patients) bro?
Limited to the ambulance. Cannot get an in-depth look into other aspects of healthcare.

Here is an amazing post about an M4's EMS experience and other clinical opportunities by /u/Igotodokterskool

Collegiate EMS

Many American colleges and universities have on-campus EMS organizations where students serve as EMRs, EMTs, and in rare cases, paramedics (NRPs).
The National Collegiate EMS Foundation (NCEMSF) unifies all collegiate EMS agencies and holds an annual conference. They also provide a guide on how to start a collegiate EMS organization if your university doesn't already have one.
There is no official list of every school with an EMS organization since new ones are being started each year, but a list of schools attending the most recent NCEMSF conference can be found here.
QRS: Many collegiate EMS organizations are Quick-Response Services. EMTs respond to calls on-foot or in a Quick-Response Vehicle (QRV) (usually a Ford Explorer or other SUV) before assessing and treating patients; however, patients cannot be transported in QRVs, thus a local ambulance company must be called to transport patients.
BLS: Basic Life Support agencies have one or more BLS ambulances staffed by EMT-Bs and may transport patients to the nearest appropriate facility. EMT-Bs can provide patient assessments, airway/breathing/circulation management, CPR/AED administration, and a limited number of medications.
ALS: Advanced Life Support agencies have one or more ALS ambulances staffed by at least one paramedic and one EMT. Paramedics may provide advanced treatment (including intubation and EKGs), and they may administer a wider variety of medications than EMTs.

ED Technician

Best for seeing many parts of healthcare in one spot. Specialists will often be called in, especially cardiologists and the neurosurgeon resident. You can spend a good amount of time with the CT and X-Ray technicians, registration staff, and ancillary workers.
Lots of physical patient contact. Can do wound care.
High interaction with nurses. Medium interaction with physicians, but depends on how nice and open they are. (They usually enjoy teaching pre-meds). During downtime you can watch them do whatever procedure, e.g. sutures, ultrasounds, the occasional lumbar puncture.
Certain responsibilities vary depending on hospital, like blood draws, splinting, cleaning a lot of rooms, and odd jobs like ring cutting.
Physically demanding.
Note that there are other, uncommon EMT jobs out there. E.g. working at the fire department, or an amusement park for a summer
If you want to keep your license for more than a few years, you’ll need to keep up with continuing education hours.

Certified Nursing Assistant (CNA)

Best way to develop bedside manner. Lots of personal care. E.g. talking to a dying patient, or talking to the family of a dead patient
Wide range of places to be hired. Can be hospital, home care, or nursing home. For hospitals, it can range from psych, to post/pre-op, to oncology, and it’s especially good for anyone already interested in a specific IM area.
Can do basic vitals. Cannot do CPR or more clinical things.
High interaction with nurses. Low interaction with physicians, with some exceptions (Like in an ICU).
Lots of monotonous dirty work, e.g. cleaning up poop and “babysitting”. Has the benefit of being humbling, an underrated trait that ADCOMS like.
Easier certification than EMT-B (but EMT-B is not difficult). Some places don’t require one.
Physically demanding.
Medium to high job availability.
Often has flexible hours.

Other technicians

Ranges from lab, phlebotomy, pharmacy, psych, optometry, EKG tech, etc.
Licensing varies for each area. Some places might not even require one, e.g. certain hospital phlebotomists. Typically based on direct clinical care. Will develop great skills in one area. Great for those with a huge interest in one specialty.
Quite limited to a small set of responsibilities. Other jobs are more recommended for pre-meds because of this.

Other jobs include nutrition, surgical assistants, public health, etc. Sometimes these jobs are better. Do your research.

Some of these certifications can also double for great volunteer experiences, e.g. volunteer EMT, work in clinics.

Certain jobs open doors to administrative/leadership positions, particularly those in hospitals.

Here is an M4's thoughts about being interesting and the intangibles you want for admissions.