Here are some tips from the pros on how to get the best results from the best commercial string trimmers:
If you want the most maneuverability and the best access to weeds and undergrowth under trees and shrubs, a straight-shaft tool is usually the better option.
For the best results on a curb, wall or tree, taper your cutting edge so that it hits the grass at an angle, pitching it towards the edge you are cutting and not away from it.
This avoids that irregular look when the edge is shorter than the rest of the lawn. For walkways, try to hold the weed wacker strings vertical to the ground and walk along the edge for a clean, sharp result.
Walk on the walkway with the weed wacker facing the grass so that debris land on the lawn and not the paving.
The direction of spin
As the strings are spinning, the weed eater needs to be able to throw the cuttings away from the strings to maximize the cutting effect.
When using a counter-clockwise spin, material is ejected to the left, so work in a direction where your right side is on the side closest to the edge you are cutting.
This avoids cluttering your new edge with debris as well as clogging your weed wacker.
Scythe tall grass
If you are trimming long grass or undergrowth rather than a lawn, the scything motion works best. This is when you rhythmically run the wacker in a U-shape, overlapping your rows to even out the cut.
Weeds in paving
For weeds in paving or between walkway stones, aim the wacker at the base of the weed and use short, glancing movements to strike it away at the base. Angle it so that you take the weed off at the base without damaging the strings