If you are facing any problem to compress videos in Sony Vegas like not in very good quality or big in size etc. then you have to take these steps to get rid of it.
So to do it first you need to go file menu and click render. Then choose main concept avc/aac mp4 in save as type option and then go to custom and choose custom frame size in frame size option, enter 1280 in width and 720 in height. now go to frame rate and set it to ntsc. Now go to project tab and set it to best.
That's it! it's all done and you are ready to go.