Since this is a secret achievement it's hard to know the hint that is given away by the title. This achievement is called "Blue Lightening", and it requires you to complete 1 stage in Xbox360 Mode/Double Play without using shots or bombs on Normal or higher difficulty. If you haven't figured the hint out yet based on the title of the achievement, this only requires the red fighter not to shoot or use bombs, the blue fighter can do whatever it wants.
Problem areas:
1. Controlling two ships is hard and takes practice. My recommendation is from the start fly the blue and red fighter on top of each other and fly them around together as best you can.
2. Only 1 credit available and 3 lives combined for both fighters.
3. Sometimes a power-up will lock onto the red fighter and fly towards it. Try to pick it up with the blue fighter before the red fighter gets it as it is a waste.
Helpful Aspects:
1. Bombs are combined between both fighters. If the red fighter picks up a bomb that is ok.
2. This can be done on any mission. 1-1 is the easiest and shortest so attempt it on that one.
Keep trying. Once you attempt it a few times you will get it. This achievement took me 3 tries to get.