Here are some tips from Lifehacker:
1. Audit Your Time to See How Bad the Problem Is – Find out how and where you are spending your time.
2. Get The Right Tools to Single-Task and Cut Off Your Distractions- Use applications to reduce notifications and distractions from your computer and phone; ear buds to reduce distraction by others.
3. Choose a Productivity Technique that Bolsters Your Discipline- Try several and see what works for you.
4. Are You Really Doing What You Want To Do? Focus on the task and determine if you have to do it now, or would you be more productive tackling something else right now.
For specific apps, websites, and productivity systems, go to this article.