Really depends on the company, what you are looking for, and the overall atmosphere within the company. If I were looking at college grad I would look at past experience (any internships, previous work, extracurricular activities). A college grad that was president or treasurer of their fraternity or sorority lets me know that they probably get along well with others and have some basic organizational skills. Someone that has interned is going to hopefully have some real world experience in the field.
For an admin asst or office manager you are going to want someone who is halfway decent with people, but more importantly has good organizational skills and time management. You are going to want someone who can think on their feet and outside the box when needed. You are also going to want to have someone that is reliable and will be there on time and when needed. How you screen really depends on coming up with a list of priorities such as these and looking at the individual's background/experience along with interviewing them to determine how they fit into those priorities.
Customer service reps is a high turnover field so finding someone who has been in the industry for years with the same company may prove challenging. You are going to want to find someone that is "people friendly" and good with dealing with stressful situations (angry customers, etc...). It may be easier to find someone new to the field who is good at this, as I would imagine the "burn out" rate is high for these jobs. People grow cold to customer complaints, etc... and begin treating customers poorly.
Data entry, you are going to want someone who is good at typing and can enter things quickly. A basic typing test would be good here. Depending on the level of data entry you require you may have the person doing some basic error checking along the way which entail an ability to think quickly and react accordingly.
Long story short, when coming up with the job description for these positions I would put together a wants/needs list for the type of person you desire. As you receive applications/resumes for the positions do a basic screen against those wants/needs. Remember that a need always outweighs a want. For example, if you want someone with a college degree that has X years office manager experience, you should be able to sacrifice the college degree for substantial experience in the field (especially if the experience is directly related to your industry). If you find yourself throwing away more resumes than you may have to reevaluate your wants/needs list to see what you can sacrifice (in other words your standard for needs are set to high). If you are getting to many good resumes start evaluating more on the wants side of the list.