I read an article by Mary McKinney, an Academic Career Coach, about how to have a productive summer.
1. Come up with your number one priority
Instead of working on several projects over the summer, none of which get enough time devoted to them, focus on completing one of them. Once that one is finished, perhaps you'll have time to move on to the next project.
2. Carve out time
Set aside time that is typically not available when school is in session to work on your project. Don't let other responsibilities that aren't your number one priority infringe on that time.
3. Increase your motivation
Let your partner, colleagues, friends, etc. know what you plan to accomplish during the summer. This will help motivate you since you'll want to avoid the embarrassment of not finishing.
Since my own summer has been horribly, unproductive so far I am going to try and do this. I have like three things I really need to finish, but instead of stressing over them all at once and not getting any of them done. I'll set my priorities and work on them one at a time, during a certain part of my day, and I won't let anything interfere with it.