Clear a wide path. A path must be at least 36 inches to allow wheelchairs to pass. However, this does not account for two-way traffic. You may want to double the width of your trails or include areas that allow people to easily pass.
Smooth the path to allow wheelchair accessibility. Wheelchairs will have trouble on rocky paths with tree roots. To help wheelchairs go through, you'll need to flatten the trail. If possible, consider paving the way.
Avoid a large slope. Wheelchair users need a gradual slope, if any, to allow them to go up and avoid a runaway wheelchair situation, where they cannot stop the wheelchair from rolling.
Create resting areas. Hiking in a wheelchair can be much more difficult than walking it--for both the person in the wheelchair and a companion pushing it. Create areas that break off of the path that can allow the user to rest without getting in the way of those still hiking.
Remove any obstacles from the path. Be aware of large branches or other items that could be obstructing the path. A wheelchair user may not be able to hold this out of the way the same way that a more able-bodied person could.