The thing that works best for me is to create somewhat arbitrary deadlines for myself. I am self-employed and work from home. My days have almost no structure at all unless I create it for myself. So that's what I do... create structure.

What do you need to get done over the summer? Break it down by what you need to get done each month, each week, each day. Be realistic and give yourself wiggle room to make up for lost time, unexpected delays, or disruptions.

So, now you know what you need to accomplish each day! Take that seriously. And keep a day planner or a calendar where you can check off tasks and chunks of work you've completed. Watching yourself tick off accomplishments will keep you motivated and (alternately) watching uncompleted tasks start to pile up will motivate you to buckle down and quit procrastinating.

Another big one is getting yourself on a schedule and sticking to it. Go to bed at the same time each night. Wake up at the same time each morning. And get to work at the same time each day. Personally, I like to get to work first thing in the morning because having the afternoon/evening to myself to relax once I've accomplished all of my work for the day is a good motivator for me to get to work and keep working until my goal for the day is met.