Choose an organising idea: one factory's grades, one escapement's development, one city's makers, one decade, one complication, or the transition from pocket to wrist. The idea supplies the reason to buy and the reason to decline.
A coherent theme also makes gaps visible. If the aim is to show the lever escapement's spread, the missing example is obvious in a way that it never is in a general accumulation.
Document as you go. Record each object's markings, measurements, condition by component, purchase source and date, service history and the sources consulted; photograph the movement, dial, case marks and any paperwork.
Keep the paper with the object. Inspection cards, service receipts, original boxes, certificates and correspondence are evidence, and their loss cannot be repaired by later research.
Write your own catalogue entries. Stating what is verified, what is estimated and what remains unknown for each piece turns a collection into a body of research that outlasts its owner.