What effects do mindfulness/meditation have on LDing?

Topic.

In short, they increase your awareness.
Aside from great relaxation which is important for techniques such as WILD and MILD, they train your mind to be aware of what is happening around you (external awareness) and of your physical sensations, feelings, emotions (internal awareness). When you practice and this awareness enough, it makes techniques like ADA and Lucid Living easier. Eventually it becomes second nature and transfers to your subconscious mind, dramatically increasing your chances of having a DILD.
Lucid dreamers who are practicing meditation and mindfulness will find their dreams will become more vivid and they will be more aware that they are dreaming, making it easier for them to stabilise and control their dreams.

So for best results, be sure to include meditation in your daily practice.
Good luck :)