First, make sure that everything is locked up as tightly as possible. Leaving your door unlocked may seem silly, but you cannot forget things like windows even if they are on the second floor. While most criminals don't carry their own ladders around, some can find items that may allow them access to areas that you may not have thought accessible. Even if there is a screen down and the window is locked, you never know if your routine has been monitored to see if you have a habit of leaving anything unlocked. Don't leave this to chance.
It is always a good idea to keep any curtains or blinds closed as well while you are gone. If someone could look into your apartment and see if you are home or not, they can also see if you have something they would want to take. Having a light on a timer switch is always a good idea as well, since it gives the appearance from the outside that someone is home even if you are thousands of miles away.
We also suggest that if at all possible, you have a neighbor look after your place while you are gone. Even just a glance out the window every morning may be enough to alert someone to anything suspicious. There's no need to keep binoculars trained on your door, but a cautious eye can go quite a long way. Having someone keep an eye out for your house and belongings while you're gone can help you to sleep better while you are out of the area. You never know when someone may be planning to force their way into your home while you're gone.