Always read both choices even if the first seems to be the logical one to take. The second choice may be even better! A specimen may not fit exactly all the characteristics given, or you may not have all the parts needed (e.g. both fruits and flowers) to fit the description. In such cases, pick the choice that most nearly matches the specimen you have. Bear in mind the natural variability inherent in living organisms.

Be sure you understand the meaning of the terms involved in the descriptions. Do not guess. Use a glossary to review definitions of terms with which you are not familiar.

When measurements are given, use a calibrated scale (like the one printed on the inside back cover of many field guides) to measure your specimen. Do not guess.

When very small objects are concerned, use a hand lens of sufficient magnifying power to show clearly the feature you need to see.

Since living organisms are always somewhat variable, do not base your conclusion on a single observation. Arrive at an average by studying several parts or specimens. Do not base your identification on an unusual or aberrant specimen.

As in following a road map, if the choice of which route to take is not clear, or if you are unable to make a choice because you do not have enough information, try both choices, arrive at two possible answers by doing so, and then read the more detailed descriptions for each species in order to make your final choice.

Finally, having arrived at an answer in a key, do not accept this as absolutely reliable. Carefully check the more-detailed, written description of the plant or animal to see if it agrees with the unknown specimen. If there is not agreement between the written description and/or illustration and the unknown specimen, then an error has been made somewhere, either in the key or in your use of the key.

Be sure also to read the descriptions of the geographic range of the species you have identified, to be sure it can occur where you believe you have found it. Although plants and animals can be found out of their normal geographic ranges, identification of such individuals should be done with extra special care, since it might represent an important range extension for the species. Alternatively, you may have made a mistake somewhere in the key and need to double-check your identification more carefully.