There are some assignments that will require you to have experience, either in a specific field, or as a seasoned house-sitter. If there are horses involved, you may be required to have equestrian experience or have had previous house sitting experience taking care of horses. Some house sits require handyman services or for someone with experience with maintaining a swimming pool. Gardening is often a skill that is requested with some requiring 'expert' green fingers! While you may be looking for a challenge, and would like to try your hand at something different, be sure to discuss your experience with the host beforehand.
Starting off with small assignments that only require care of small household pets and patio plants is prudent to obtain the experience and testimonials required for others to consider you for larger, more varied positions.