1) Try not to use Sony Vegas presets, the outer glow for text should never be used, sticking to white text on a black background is simply nice
2) the 'border' for the video which faded it a bit ( forgot the name of the preset ) shouldn't be used throughout the whole video, just make the clip fit the whole YT screen (idk what the YT player's size is, don't make it widescreen though)
3) when using manually put gunshot sounds, try to make it match the speed of the gun shooting (rof/rate of fire)
4) try not to show dead time (you not killing, small movements, no action or any suspense)
and make sure at the end of the sony vegas timeline up until the last track (be it audio or video) rid of anything so it doesn't leave a blackscreen like in this video here.