How can I use "thinning shears" to trim the layers in my hair?

I had a hairdresser show me the trick once, but I can't find a reference with pictures anywhere online. I would like to clean up my layers in between haircuts, and was told its hard to screw up with thinning shears. Please Advise!

How can I use "thinning shears" to trim the layers in my hair?

I wouldn't suggest thinning shears, unless your skilled, they are only to remove bulk, not clean up layers, if you cut too deep, you will remove to much hair,and lose volume, just go through your hair and remove about an inch all over, very simple, use hair clips to hold the hair back you already cut, but just clip the same amount off all over