You learn to recognise blue nevi, Congenital nevi , Spitz nevi, Reed nevi, dermal nevi and rarer lesions such as combined nevi, deep penetrating nevi and lastly atypical (dysplastic) nevi.
Seborrhoeic keratoses vary a lot dermatoscopically and you just need to look at a lot clinically to be aware of the various patterns dermatoscopic.
Lentigenes are very common particularly on the face, back and sun exposed arms. Uniform colour and generally symetrical but may have a network or pseudonetwork on the face and sometimes grey dots of regression. They are not melanocytic lesions.
If you cant confidently diagnose something as a nevus, seb k or lentigene then it is a melanoma until proven otherwise after excision.
Other tumours you will see commonly are actinic keratoses, SCCs both invasive and in situ and various types of basal cell carcinomas. You just have to learn the dermatoscopic features of each of them.
Benign tumours are sebaceous hyperplasia and adenoma, dermatofibroma, pilomatricoma, wart, molluscum, accessory nipple, clear cell acanthoma, prurigo nodule. They each have some characteristic dermatoscopic features to allow you to diagnose them.
Nail tumours including onychopapilloma and onychomatricoma can also be recognised with the dermatoscope. Subungual tumours including warts, SCC and melanoma are often difficult to separate clinically but along with a glomus tumour the dermatoscope can help.
Vascular lesions such as Campbell de morgan spots, Pyogenic granuloma, Kaposi's sarcoma and angiosarcoma have dermatoscopic features as do angiokeratomas.
Rarer tumours such as AFX, DFSP, Merkel cell carcinoma and Desmoplastic melanoma can be difficult to diagnose with the dermatoscope alone.
Medical Dermatology is best learned at a clinical lesion level but there are times when a dermatoscope helps.
