Hi @Moshe Aharoni , congrats on the first purchase! Big step.
I just started in student rentals myself earlier this year. One thing I learned my first time around the block is to get an idea of when students look for housing for upcoming school years. If housing is hot around a certain university, properties may be leased up for 2017/2018 school year in the fall of 2016. But most likely there should always be waves of activity in the spring and maybe once more in the summer for those procrastinators. So make sure all your postings (especially on craigslist) stay up to date because you never know when someone will be searching. Reach out to any past-students (or even better current students) or other landlords to understand when these waves come. You'll always want to make sure your rates are competitive especially if you're getting close to end of searching process. No income for the year would be brutal to the bottom-line so it may make sense to drop your rates in order to secure cash flow.
As far as summer rental period - use it to your advantage.. offer 9-month leases to students as a slightly higher cost/month than 12-month (where 9 month total costs < 12 month total costs) but also grab that summer rental income. I assume the turnover/maintenance will be the thing to worry about there over the summer.
See if the university has postings on its website. The university where I invest does but we've gotten 1 hit on that compared to 20+ on craigslist.