Physicians Assistant

Overall GPA.
Psychology GPA minor (if you have one).
GPA last two years in college GPA.
Maintaining a high GPA from your freshman year on
If you do not get an A or B in a course you should probably repeat the course.

You can get involved in research as part of Independent study course and thus earn credit hours and possibly increase your GPA if it counts as a graded course or volunteer.
Get even more involved in research by doing a Senior Honors thesis or some other research where you can get your name on a conference presentation or journal publication.
This kind of recognition is rare for an undergraduate and will really boost your standing when you apply to PA school.
An advantage to working in a lab is that you get to know a faculty member who can write you a strong letter of recommendation when you are ready to apply to graduate school. Given you need more than one letter of recommendation, it is probably best to work in two different labs as an undergraduate.

By doing an internship you can again show your high level of motivation for PA school.
This internship can be with an on-campus clinic/organization, or off-campus clinic/organization dealing with medicine.

There are a number of skills you can develop in addition to what you learn in classes and by conducting research-- computers, writing, and oral communication skills.

Among others, you can volunteer at a medical hospital, clinic, or a setting that involves the sick or infirmed.
This involvement demonstrates a high level of motivation and interest in medicine. Any involvement just adds to your overall record and makes you a more competitive applicant.

It is not critical that you are employed in a medical (such as those listed above) as an undergraduate, but if you can get such a job that is a real bonus.
Adds to your overall record and makes you a more competitive applicant.

Shadowing gives you insight into the life of a medical professional.
Demonstrates a high level of motivation and interest in a medical profession.

PA schools vary in what entrance exam they require. Most will ask for the GRE (Graduate Record Examination), a few recommend taking the MCAT (Medical College Admissions Test), and there are some that will let you use MCAT scores instead of GRE scores.
The GRE
The GRE is the standardized exam that almost everyone who applies to graduate school must take. It can be viewed as the “graduate SAT or ACT”. Because it is a standardized exam that means everyone across the country and even in the world takes the same exam in the same way on the computer.
Also, be aware that most schools will want you to take the “regular” GRE that includes a verbal component, a quantitative component, and an analytical component.
Some schools may want you to take a subject GRE exam in Psychology. Because of this, it is probably a good idea to keep your textbooks from your Psychology courses to help with your studying.
Your GRE scores are extremely important. Because the GREs are a standardized test, the argument is that this score allows each graduate school selection committee to compare your score in an equal fashion against all other applicants.
This gets even more important if you are going to a college that is perceived as less strong academically. For example, if you go to the University of Kentucky (U.S. News and World Report college ranking of 129) and get a GRE score of 2200 and a student going to Harvard (U.S. News and World Report college ranking of 2) gets a GRE score of 2000 your application will likely be viewed as quite strong.
Another way GRE scores can work for you is if you have only mediocre grades (e.g., a 3.20 overall GPA), but you score really high on the GREs your high score can, in effect, offset those modest grades.
As far as preparing for the GRE, some argue that you should begin preparing for the GRE by your sophomore year. This would involve using GRE practice books and software on a regular basis. One reason to use GRE software is that, because the GRE is only given on computer, you should familiarize yourself with this type of exam format.
As far as the three specific parts of the GRE, let’s talk about each. First, there is math. If you are pretty good in math and plan on taking at least some Math courses in college, you are putting yourself in a good position as you begin to study. However, if you do not feel you are good in math and have no plans to take a Math course in college beyond a freshman Algebra course you probably need to rethink your plans and think about either taking more Math courses or get someone to tutor you on the math that will be covered in the GRE. Of course, doing a lot of studying will help, but having additional resources will serve you well.
Next, there is the analytical component. The same issues here apply as with math. There are courses you can take that will help you out with this section, like Logic. Strongly consider taking courses like this so you can be better prepared for the GRE.
Finally, the verbal component of the GRE requires you to have a strong background in English. You may think you know the language well, but the GRE asks some pretty tough questions ranging from word definitions to comprehension of stories. One piece of advice is to Read, Read, Read. Over the years we have seen many bright students suffer on their verbal GRE scores because they just are not exposed enough to verbal information. For example, one of the best ways you can learn new words is by reading these words in a news article or novel.
MCAT
The MCAT is the standardized exam that almost everyone who applies to medical school must take.at is the MCAT? If you are not clear about the MCAT, you must understand that this is the standardized exam that almost everyone who applies to medical school must take. It can be viewed as the “medical SAT or ACT”. Because it is a standardized exam that means everyone across the country and even in the world takes the same exam in the same way.
Your MCAT scores are extremely important. Because the MCATs are a standardized test, the argument is that this score allows each graduate school selection committee to compare your score in an equal fashion against all other applicants.
This gets even more important if you are going to a college that is perceived as less strong academically. For example, if you go to the University of Kentucky (U.S. News and World Report college ranking of 129) and get a high MCAT score and a student going to Harvard (U.S. News and World Report college ranking of 2) gets a low MCAT score your application will likely be viewed as quite strong.
Another way MCAT scores can work for you is if you have only mediocre grades (e.g., a 3.20 overall GPA), but you score really high on the GREs your high score can, in effect, offset those modest grades.
As far as preparing for the MCAT, some argue that you should begin preparing for the MCAT by your sophomore year. This would involve using MCAT practice books and software on a regular basis. You might also consider taking an MCAT course from a company like Princeton Review or Kaplan.

It is very important that you start to interact with Professors right away. This can occur by making contributions in class or just going up to your Professors and having a conversation about issues in the field.
These interactions can lead to being able to work in a Professor’s research lab, hearing about job opening that may be available in the Psychology department, and letters of recommendations for graduate school.
Remember, if a faculty member does not really know you or had you in one class, there is a lower likelihood that the Professor will agree to write a letter for you or knows you well enough to write a letter.
There are two important things to keep in mind with regard to letters of recommendation. First, a short letter of recommendation from a faculty member who does not know you well can sometimes be worse than no letter at all. Second, It is almost always better to have a letter of recommendation from a full-time Professor than an Instructor. For better or worse, the former simply has higher status than the latter.

Here is an article that discuss issues related to those above:

http://wiselikeus.com/collegewise/2010/04/10-things-every-future-premed-should-know.html