Some of my work - could use tips

[bloomy]

Some stuff I've done. I always struggle with shadows, lighting, and reflection. I'd love some tips.
I use Affinity Photo.
Also, all photos I use from getting the photo to adding to it is from Unsplash.

Shadow of the guy in the first photo could use some work
In the second photo, the spaceman in center frame was already there, I added the other two.

 

[IamSam]

Hello and welcome to PSG!

I always struggle with shadows, lighting, and reflection. I'd love some tips.

You have to carefully evaluate the direction of the light source in the primary image in which you are going to be adding a subject(s) in your composite.

In both of these composites, the light source seems to be coming from the left rear and rear of the primary images. In both images, the added subjects are not lit the same as the BG image you placed them in.

In the first comp, had you inverted the boy and placed him on the right side of the BG image, it may have worked out better. The fish are close enough that they would be OK with maybe a few minor touches.

The two added men in the second comp are lit from the front while the light source is coming from behind. (There will be those that will state that there could have been a secondary light source.........but the BG images do not imply a secondary light source.)

Al in all, great ideas!!! Thanks for sharing!!!!