There are a lot of different ways to do this, here are a couple to get you started.
You could use the effect - Perspective > Drop Shadow and set the distance to 0 and just increase the softness to get the desired effect.
Another method would be to go to Layer > Layer Styles and apply the Photoshop drop shadow on to your layer and adjust to taste. Also you could just use the outer glow effect.
You could also use a stroke on your text/object layers by using 2 layers. Add a stroke to the bottom layer and blur that. But if you are making a lot of changes, you will want to figure out precomps, parenting and some expressions, so that when you make a change to your master layer, it updates your blur layer.
"I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work."
---THOMAS EDISON on inventing the light bulb.