Making videos in STK takes practice and time to learn, but there are lots of techniques you can use to produce high quality, realistic, technical animations.
To get started, go through the STK Fundamentals on help.agi.com. The final lesson shows you how to record basic STK animations. http://help.agi.com/stk/index.htm#training/Day1Overview.htm
Here’s an additional video that goes into more detail: Creating Videos in STK
Here’s an advanced video that goes into even more detail: Using Advanced Techniques in STK Moviemaking
It is important to use the best 3D models when recording videos. There are several models available for download from AGI's website here:agi.com/models
You can also convert your own models for use in STK:FAQ: How to convert CAD models for use in STK
It is also important to have high resolution terrain and imagery. STK has streaming terrain and imagery, but if you can't connect to the internet, you can download files from here:AGI.com > Support > Supporting STK Data > External Data Sources
Another technique to making more realistic videos is to add model articulations. This video shows how to use articulations: Creating Articulations with the Movie Timeline Tool