Very simple trick....Dont shoot grass into the beds!
Mow perimiter laps of the lawn blowing the grass in when you start. I mow 2 laps but the distance that your mowr discharges may vary. I also have a OCDC so I close that when near beds.
Also when doing your back and forths you can start at the left of the lawn or the right(when mowing stripes vertical to the road). If there is a flower bed along the front of the house, i will always mow left to right. That makes it so when I am turning around by the beds the chuts is pointed into the lawn, rather than at the bed.
Trimmer heads turn counter clockwise. If you trim with the 12-3 section of the trimmer it will throw the clippings foward. If you contact the grass in the 6-9 section it will throw the clippings backwards. I walk backwards as I trim, and trim with the 6-9 oclock section of the trimmer. This throws the trimmings away from the beds.
When all done use you blower and remove any stray clippings.