Ummmm...not much to say really.
Use it only on concrete edges or bed edges, not against asphalt, wood, plastic paver retainers or metal edging. If it's one with a wheel put the wheel on the hard surface. I've seen many recommned using them while walking backwards with I prefer going forward most of the time. Sometimes I work it back and forth a bit. Use a blower to blow out the crack when you're done. Use full throttle. If the soil is wet it may clog up in the guard, but that depends on your unit. Mine (Shindaiwa) is very prone to clogging in wet soils. Make sure to have spare blades on hand, they wear rather quickly.