One of the biggest problems I see with students, especially in group work, or with people in general, in regards to making plans or coming up with ideas, is the lack of "yes, and..." in their conversations. Most of us, in the real world, are quick to reject an idea rather than allow the originator more time to expand it. The thing about ideas is that they're often not perfect on the first around. A little more "yes and..." in the conversation can really improve the dynamic of a group trying to come up with a new idea.
Of course, sometimes "yes and..." isn't practical, but it's cousin "no but..." often works just as well. Sometimes saying "yes" isn't an option, but it's almost always possible to offer and alternative. If someone invites you to go hiking, but you think it's ridiculous to walk around in the words, don't respond with simply an excuse, offer something else. If you're forced to cancel plans, rather than begging for forgiveness or suggesting a vague "rain check", solve the problem immediately. Contrary to popular belief, saying "no" isn't what kills a conversation...but failing to offer an alternative certainly will.
So as you go through summer, whether you're still at work, or enjoying the time offer, don't forget to respond with a "yes and..." or a "no but..." when given the choice. The first is ideal, but the second can work just as well. Both are far superior to their enemies: Excuses.