Which of the "qualities" are you trying to improve?
If it is "picture quality", it is totaly dependent on the source. Video editing programs can't make pixels that don't exist. The basics are getting good source footage, setting the editing project to match and outputing the finished result with also matched settings. The current most common standard is "HD" at 1920x1080 pixels. "4K" is a higher standard but not yet universal.
What is your source video and what are its exact specs?
Open one of your original video clips in the free download MediaInfo. In MediaInfo, set View to Text and then copy this text and paste it to this forum. Once we've seen the specs of your source we can recommend "step by step" the optimal workflow to give you the best results.