In an effort to combat "cheaters" I make 2-3 versions of the test.  Version "A" is the master and I use versions "B" and "C" for the students.  I simply scramble the questions and stack them "B-C-B-C."  I do not let them that there is more than one version of the test.  They usually figure it out pretty quickly or their own.  This is usually enough to keep their eyes on their own test.  

I use differnt renditions of the exam and I keep the students separated by an emptly chair whenever possible.   I warn them in advance that phones should be put away during tests and that any phone out during the test will be considered cheating as well as any conversations during tests. 

You need to set your expectations on day one concerning academic dishonesty.  Adhere to your institution's policies and do not be afriad to implement your own.  At times you will have to use a cheating student as an example to demonstrate that it will not be tolerated in your classroom.

These are very good points. Some students use their cell phones to text each other during a test. As you walk their way, they hide their phones or say they need them for doing calculations. We had to band the use of cell phones which helped put a stop to the cheating.