I just pay attention to something, but it's usually quite hard for me to fall asleep at night, so I guess I can maintain conciousness quite easily. So try observing the back of your eyes, your breathing, or the sensation of sinking (or whatever is going on).
Also, autosuggestion is a good way to stay focused on something, so perhaps say "I will remain concious" over and over.
WILDs are hard, don't worry if you don't have success, just keep trying!