In most cases, the ideal candidate will have at least some exposure and experience in the areas that the job entails. Sometimes it is difficult to find individuals with just the right experience, especially if your industry is specialized or relatively new. When creating experience requirements for a position, you can demand specific experience, but that may make it more difficult to find anyone to fill a position.
Here's an alternative. You may want, instead, to consider making the experience requirement broader, especially for entry-level positions. For example, if you need an administrative assistant who can type, answer phones, and file, chances are you'll need someone with good organizational skills. Instead of requiring one year of clerical duties, you might make the experience requirement broader, as in one year of experience in general office work or even one year of experience in a high-pressure, multi-task environment. You might find a person who does not have clerical experience, per se, but a person who was, for example, an assistant manager at a department store or a server in a restaurant who might have some of the same set of skills and abilities.
The important thing is not to define your experience qualifications so strictly that people who could do the job are disqualified.