This step, in my opinion, has the biggest impact on making your effect look realistic!We want the explosion to push elements out of the way, to have some actual power.
For this, film yourself throwing or pulling or pushing any elements around the centre of explosion out of the way as if they were hit by the shockwave. I like actually adding a few loose elements that I can then fling around, e.g. I added the cardboard box, the bucket and a few pieces of wood
Then, mask out these elements using animated masks (or the rotobrush tool) and add them on top of your footage at the correct point in time. This will make them seem to be flung away by the pressure of the explosion.
In the shot above you see the cardboard and buckets still standing on the ground even though we see the masked out elements flying away. At the moment of the explosion you will need to cover up the elements standing on the ground so it doesn't look like they are duplicating.
For this, you can simply use a shot of your scene without any elements in it. Mask out the area around your dynamic elements and place this 'cover up' layer on top of your jump footage and underneath all the dynamic elements. Ensure the layer becomes visible the moment all the dynamic elements do.
If your cover up layer does not sit right in the shot - in my case the lighting had changed slightly from when I started filming - you can fix this by adding a simple curves adjustment to the layer I brought the brightness down just a touch to make it sit nicely in the scene.
Pre-compose all layers by selecting them all and selecting Layer -> Pre-compose. Select to move all attributes into the new composition and click OK.
Next, add your explosion stock footage element!I like to trim off the first few frames of these elements usually just so the explosion appears a bit more instantaneously and thus conveys a little more power.
Cut out any elements that would obscure your explosion. I have cut out the tree trunk and a little bit of the ground to make the stock footage appear to sit on the ground.
Add a glow effect and increase the radius to somewhere around 200 so the stock footage gets a nice intense glow.
If required, add a saturation effect to your explosion stock footage to blend it nicely into the scene. I brought the saturation down a little because the stock footage seemed a bit too red in my opinion
Again, pre-compose all layers.
Make sure the intensity and duration of the lighting matches your explosion
Now let's add a cool shock wave to the explosion!