There is implicitly more dangerous about camping on your own. That is to say that the probability of something going wrong is no worse than with more than one person, in fact one person is less likely to encounter a problem than two from a pure probability theory perspective. The exception is a collaborative exercise like a river crossing, but that's another matter.
The thing we have to consider when we're on our own is the impact of something going wrong. That is to say how bad it is. When something does go wrong on your own, there is nobody to help you lower the impact of a problem.
From a risk management perspective we would therefore want to:
- Reduce probability of incident
- Reduce impact of incident
The incidents that are more likely to occur when camping are:
- getting lost
To reduce the probability of getting lost, ensure that you have a good plan, map, compass and keep a constant log of where you are and where you're heading. If you can plan to reduce the likelihood of getting lost by choosing routes with more well defined paths or more obvious landscape features (mountains and water normally), then all the better. This strategy is based around you reducing your exposure to the chances of getting lost. Clearly the purest strategy is to camp next to roads, but that's pretty boring. However, camping on a route which is perpendicular to (say South of) a straight (East/West) road will give you the opportunity to head in one direction (North) and return to that road no matter how East/West you are of your intended course.
To reduce the probability of injury, good quality equipment appropriate for the terrain will be ideal. Clearly, reducing exposure to high risk features such and fast flowing water and steep, loose rock faces will reduce the chances of injury. Strategies such as grass disturbance mentioned by another poster will also help.
To reduce the impact of injury a good first aid kit is essential. As a small cut (low impact generally) can soon become infected (high impact) if not treated. More immediately life threatening injuries can sometimes be managed personally, but loss of mobility and consciousness will often be what prevents you from self help in these situations.
You will need to have an idea how "far from help" you are. This is more of a time than distance issue. Time can increase the impact of injury and injury can increase the time it takes to help yourself, specifically in terms of self extraction.
Remember, help can only come if they know you need it and they will also need to know where your position. If you cannot readily communicate and you do not have a good idea of your position if you can communicate, then you will increase the time it takes to find you and thus increase the impact of the original incident. You should have a good idea about the mechanisms of communication available in your area and the available SAR services.
If you know your communication is patchy, they you can employ a "lack of communication is a problem" strategy having known check in points to a third party who knows your plan and who will communicate with rescue services on your behalf if you do not check in.
With this in mind, it's worth noting that if you have made a plan, you should stick to it. If you want to change your plan, you should let someone know. That way when the threshold of lack of communication happens and SAR gets involved, they will have the best idea where you are.
It may be that you are in a region where other people are about which you could signal to. In this case, a whistle (on your person) is a great tool as it requires little effort to blow and get at least some distance, which is nice if you've cracked your ribs for instance.
Time compounds the impact of getting lost where lack of water and food can become an issue. In these cases, you must plan for the worst. Even a one day hike can become a night camp if you get lost, so don't forget that torch.
In summary, reduce the probability of incident by reducing exposure through planning and by using good quality equipment, a plan and a log. Reduce the impact of incident by keeping essential equipment on your person and having enough equipment for survival based on how far from help you are. Have a communication strategy and stick to the plan.