hi, this doesn't look to bad.

but since you asked how to improove it... I think it would add a great deal of realism if you gave the UFO a shadow. Also since you are compositing in after effects. There is a technique called light spill. When you film a human/UFO or anything in a real environment the ambient light of that area would normaly have an effect on all objects. Sice it is a CGI UFO you'd have to cheat a little to get that effect. Anyway I am not going to explain how to do this in detail, but here's a link to a tutorial.

https://www.creativecow.net/show.php?...ill/index.html

good luck.