Being a editor requires a combination of technical skills, creative skills, and storytelling chops. Here are some tips to help you improve your video editing skills:
Learn the software: Familiarize yourself with whatever video editing tool you have access to. The basics of editing are the same across platforms. Some tools are closer to the industry standards than others, but with good editing basics even the most basic editing tool can become a weapon in the hands of a skilled user.
Understand the basics of storytelling: Have a strong understanding of storytelling techniques. Learn about the different types of shots, angles, and transitions and how to use them to not only tell but enhance a story.
Develop your own style: Experiment with different editing techniques and find your own unique style. This tip is a little harder dependent on which type of editing you do. If you're working in a studio environment with a director, more than likely you are helping to showcase the directors style and vision...not your own. However, having your own style doesn't have to mean just what's on screen. Every editor has a workflow that works for them in the edit bay. So your style may be whatever helps you achieve the best product in the end.
Practice, practice, practice: The more you edit, the better you will become. Try to edit as many different types of videos as possible.
Keep your audience in mind: Think about what they will want to see and how you can make the video interesting and engaging for them. This can be done in several different ways, it can be done by withholding information, cutting to that perfect reaction shot, dropping in that perfect piece of footage or removing scenes completely.
Stay organized: This will help you stay on top of your editing process. There's nothing worse than remembering a shot that you saw in the dailies but can't seem to find in when you need it. If you're working on longer form documentary projects, organization becomes even more crucial
Listen to feedback: Always be open to feedback from others and use it to improve your editing skills. This can be one of the hardest steps to take. Listening to other critique your work can be a unpleasant process but it doesn't need to be. Even with the seemingly unhelpful notes, look for that little bit of wisdom that could be helpful.
Remember, video editing is an art form and it takes time and practice to master it.