Because RNA is prone to digestion by a wide variety of endogenous and exogenous RNases, and because these RNases are present on almost all objects that come into contact with humans, extreme care must be taken to prevent sample contamination and degradation. Diligence and adherence to some simple rules can make the difference between an intact, clean RNA prep and degraded RNA. The overall objective is to keep the mRNA profile of your sample intact for downstream applications in order to generate meaningful data.
Don't touch anything with bare hands that will come into direct contact with RNA.
Don't breathe on samples. Some researchers even wear masks.
Don't autoclave pipette tips, as water vapor in most autoclaves contains RNases.
Don't rinse tissue stored in RNAlater prior to processing.
Don't allow frozen tissue to thaw.
Don't resuspend RNA in DEPC water if the RNA is required for certain downstream applications. Residual DEPC can inhibit some enzymes and has been shown to adversely affect RT and translation reactions.