Substances tagged with GHS labels should only be weighed in under an extractor hood. It is always important to keep the weighing place clean to avoid contaminations. Other colleagues should be informed about special exposures, for example when you are working with CMR (carcinogenic, mutagenic, reproductive toxic) substances.
It is also necessary to keep the weighing range of the scale in mind. If the weighing range is for example 10 mg to 120 g, it is not reasonable to weigh amounts below 10 mg because of the error of the scale.