Your Serger Tensions  are similar to your sewing machine.   And, like your sewing machine clean and oil your serger.  Remember to change your needles, this is much more important than on your sewing machine.  One difference is that most serger tensions are not released when the presser foot is lifted.   So make sure that you pull your thread into the tension by holding the thread before and after the tension assembly.   When adjusting your tensions always look at your left needle thread first.  That is your base for the rest of the stitch.  Set your tensions to normal ( usually about 4 ) and serge about 6 to 8 inches.   Look at your left needle thread.   It should look balanced similar to your sewing machine stitch.  Next, look at your looper threads.  They should be joining on the center of the edge  of the fabric.   If the stitch is going more to the top, loosen your upper looper tension.  If the stitch is going more to the bottom,  loosen  your lower looper tension.  Now, if you have a 4-thread serger look at your right needle stitch.   If it is coming more to the top, loosen the tension for your right needle.   If it is going more to the bottom, tighten the tension for your right needle.   Two things to remember: You should always try and keep your tensions on your serger as loose as possible.   This will cut down on thread breakage.  And, always use good thread.   The serger stitch is being formed by all the 2, 3, 4, or 5 threads being used.   If one of those threads is not good and consistent, your could have a tension nightmare.   
If, you are still having a problem after all of this,  check our Thread and Needle pages for more help.   And if all else fails,  call your local dealer for help.  Keeping in mind that there is probably something more than a tension problem.  You might even have a damaged part.   So, you might just consider having a service done.   In fact, it is a good idea to have your machine (sewing machine and/or serger ) serviced every 3 to 5 years.