Rinse the freshly washed panel off with fresh water, then liberally spray the Bugger Off all over the still wet, affected panels. Focus on where the bugs are most concentrated. Let the product sit for about a minute or two, spraying a little extra if it looks like it's drying. Then fold the DeBugger cloth in half, totally wet it and gently rub off the bug marks from the car. Keep turning the cloth to a clean side with each wipe, and rinse the bugs off with water once it gets full.
Rinse the cloth out in fresh water and wipe over the area again, before finally rinsing the panel clean with fresh water. Then chamois/microfibre towel dry the front of the car and you're done.
I know plenty of professional detailers who like to use a pressure washer for this job, using the strong stream of water to remove the Bugger Off and all the bugs with it. I must say it does this job well. However, the bugs that remain can get pushed back into the grill and other innards of the car, meaning there can be more cleaning later, in areas that are very difficult to access. So try and make sure the water pressure is directed away from those areas.