The first thing you need to do is look at the amount of subscribers you currently have, the average amount of views you are getting per video, and establish a connection (if any) between your videos that have done poorly and your videos than have gotten many more views than your average.
Now that you know where you are starting from and what may or may not have made your past videos successful, you can make some changes to hopefully get those coveted views!
First off many popular YouTuber's have a fan base that extends from the realm of YouTube. They have facebook, twitter, and sometimes even their own website to help promote their content. Start by making a facebook and then a twitter and asking your current subscribers to "like" and "follow" you and invite their friends. Viewers like a sense of community and if you answer their questions and keep them updated about your life or video progress/ideas they will be happier.
Second, you should consider going through your videos and adding annotations that say things like "subscribe for more content" or "press the like button to help me out". Simple visual encouragement and reminders like these can definitely help your popularity over time.
Another idea is to make a video solely dedicated to asking for help from your subscribers. Tell them you plan on uploading better content more frequently in the weeks to come and you need their help by telling their friends about you and by linking your videos on their social networking sites.
One technique many of the top YouTuber's of today use is to form relationships with other high profile accounts. This allows one account to expose its fan base to others and in return get attention from their loyal viewer's! This can be a GREAT way to get to the next level in YouTube success. Perhaps start with people you know in the real world who have YouTube accounts. Your old soccer teammate may have started uploading videos of him playing the guitar 5 years ago and now he has thousands of viewers. Simply tapping into his fans in exchange for featuring him on your page would be a great way to mutually benefit. You never know which of your friends or acquaintances may be a YouTuber just like you- do your research and find out! Afterwards, you can begin sending emails or reaching out to other YouTubers you may have never met and attempt to form a relationship with them, you'll never know if you don't try!
Next, let us focus on your less popular videos and define some aspects of them and ask some questions. What is the title of the video? Is it accurate in regards to its content? Does the title catch a possible viewer's attention and entice them to click that play button? How long is the video (longer videos generally do not get as many views)? Is there any "down time" in the video (time where nothing funny, interesting, or related to the theme of the video occurs and may bore viewers)?
Those questions, their answers, and the thoughts they have sparked should give you some ideas of what made those videos not so popular. Everybody has their bad days or flops, now it's time to learn from yours and improve!
Perhaps you can re-edit and re-upload your old videos that don't have many views. You could try things like using better transitions and more attractive effects, shortening the overall length of the video by cutting out the irrelevant parts, and giving it a fresh new name that gets a YouTuber's attention. Don't forget to add links to your new facebook and twitter accounts in the description box and ask for support! Perhaps simply deleting your oldest or most unpopular videos will be a good way to do some "spring cleaning" on your account and not deter anybody who checks out your YouTube page and who may run away by seeing your old unpopular videos.
Now that you've established what is to come in the future and you have deleted or re-edited your old content, it's time to focus on the present.
With each new video you must really push your creativity to have the most original and entertaining content you possibly can. Watching other successful YouTubers and learning from them may be a good idea but certainly do not copy anything they do! Depending on the type of videos you produce you should now become more serious with things like camera angles, scenes, scripts, lighting, audio/microphone equipment, and editing and transition skills and techniques- your viewers will really be impressed!
Finally, after you have overhauled your channel, reached out to your current viewers by branching out into the social networking world, and have begun making better content than you ever have it is time to really do all that you can to get more views and popularity.
You must be your own hype man! EVERY time you post on twitter or facebook you have to remind your fans to subscribe, like, and share your videos to their friends. Reminding them to simply post your videos as their facebook statuses and tag friends they think would like your videos or to re-tweet your links will certainly increase your popularity and bring in new viewers. Remember, things will begin to grow exponentially as more fans and subscribers share with their friends and then their friends!
One of the final ways to get more views on YouTube videos is to start investing some capital (money) into your future. Consider making ads for your content and featuring them on other YouTube videos. Remember- the more people who see and hear your name the more awareness!
All in all, a combination of many techniques must be used to get more YouTube hits. But in the end- it's your determination and hard work over time that will benefit you most.