My first suggestion is to establish what type of relief position you are suited to.
For example, smaller operations are looking for a more hands on approach which will include tasks such as room prep, bed making and some general cleaning as well as basic managerial clerical, whereas larger or busy premises may just be looking for managerial skills.
Too many relief managers lose me when they start talking about their wealth of business accumen, and how they can improve your business.
Many operators are just looking for someone to hold the reins while they take short breaks.
It would be interesting to get others views, so I hope that some others may weigh in to your query.

Once you have worked on your direction, market yourself to those businesses within your area of availability,
dont try to mass market yourself, pick a few and build up to the amount you would like to work, as it is no good having relief managers that are never available and you will soon be dropped.