Depends on the videos, if you're vlogging then make sure to NEVER have a awkward silence (unless it's for comedic sake), This is where jump cuts come in, where you cut to a point where you start talking again (only once every 7-10 seconds or longer). Make sure to remove any bloopers you make. Only add background music when things start to get more intense, and make it quiet so we can still hear you. (Make sure the music isn't copyrighted). After watching your video, i'd say get some light on your face (lamp or something), remove the "Um"s and DEFINITELY DEFINITELY Make a script before hand, so you know exactly what to say, when to say it and to make sure you don't miss anything out when talking. just place the script near your camera, learn the lines then look at the camera and say it. then just edit out all the useless stuff.
Tiny things to fix when you feel like are to get a better camera and put some posters up behind you.
If you want to do a voice over a game when talking about news n stuff, then just do the same as above but remove the music.
Also don't quit after a few months, some of the biggest youtubers don't even gain their first 1000 subs in their first year of making video's.