When you wake up, write down anything you feel. Even if it's not a dream. Sometimes I wake up with about one fragment (I never "don't have a dream") but I'll wake up with a song playing on a loop in my head. Or I can't get a scene out of my head, or I woke up with a strange thought. Write down anything and everything, eventually yout mind will realise you want to remember them and you'll start to get fragments. Keep building on it and your recall, then you vividness will improve

And like the others said, you need to be able to recall your dreams before you attempt to WILD. It's why dream journals are so important