It's a good start, CK! You got some good technical skills to work with, you just wanna open up the storytelling aspect of it. While it's not necessary to describe every second of a story (that would actually hurt a story for a lack of focus), you always want to describe the important parts. The guards turning out to be bad guys should be a pretty big shock so don't be afraid to take your time with it, describing how they may seen not quite right and the surprise twist when they start attacking the good guys. You wanna build up the suspense a bit and put the reader on the edge of their seat, yeah? But you did a nice job for a first timer!