You could be procrastinating often. This could be because you think work or something is boring, or have no motivation. The only thing you can really do it to focus on what you want. No one else can really do things for you, or make you want to do them. If you want a good grade, get that assignment done! If you have things you need/ want to do, you need to focus on what you have to do to get there. Doing random things that don't affect anything are useless, because you never progress. Put your mind to it and work hard!