Procrastination is easy because there is an immediate reward (feeling better) as soon as we abandon a distasteful task. On the other hand, it's possible to reward good habits; finding ways to reward good study habits is important for handling procrastination.
It's natural to have negative feelings when starting a study session, even for subjects we like. One way to get past those feelings is with positive self-talk: "Don't worry it won't last, just get started." In addition, setting a time period and sticking with it will help a lot. For starters try 25 or 30 minutes of focused work, then take a little break with a reward, like a snack or some youtube surfing.
Another, even more effective, method is to focus on process instead of product. Process means the actions and habits of studying, whereas product is what you are actually working on, like an assignment that's due soon. So instead of thinking constantly about what must be done, focus on the small steps that make up the larger task. By doing this you will be less judgemental with yourself about your progress, and more able to relax and get into the work.
You must also become accustomed to letting disturbances blow by and not be annoyed by them. To become good at this, avoid distractions as much as possible. The Pomodoro Method is a very good way to apply all of these ideas.
Be aware of cues, such as location, time of day, how you feel and your emotional reactions that lead to distraction and procrastination. Develop a productive routine, which may involve setting up a quiet place to study, leaving your phone elsewhere and resisting web surfing if you have to look something up. Better yet, if you find need to look something up online make a note of it for later and continue studying by switching to something else (which is also an effective learning technique called interleaving). Don't forget to reward yourself when you have successfully executed your new study routine. This helps to rewire your brain with study good habits. Keep track of things that work so your new routines can evolve and get better.
Lastly, there's no substitute for positive thinking; you have to believe that your new routine and habits will help. It may take some time, but stick with it and it will become easier and easier.