I'm very fascinated with watch collecting/investing, but I'm not the most knowledgable enthusiast. What's the best way to learn about the history of watches and how do I determine the rarity of a watch for investment?
No worries Matt. Every expert has been inexperienced, every blogger has been blog-less, and every dealer has had, at one time, no watches to sell. That's life! But I'd be more than happy to give you a few tips on how to go from an unseasoned collector to a full-fledged W.I.S. (Watch Idiot Savant). Also, to answer your question in its entirety, I will additionally explain how to discern the rarity of a timepiece.
Hit the Books
Most guys I work with own A LOT of books: Rolex books, Patek books, Longines books, Omega books, and anything else you could imagine. Why? Well, these books are tangible and reliable sources for information pertaining to specific brands or, in some instances, specific watches. Notable texts are Guido Mondani's Rolex Daytona Story, Grégoire Rossier and Anthony Marquié's Moonwatch Only, John Goldberger's Longines Watches, and the fantastic Complete Price Guide To Watches.
Attending an auction equals heading home with possibly the best vintage and modern watch book ever invented, a catalogue. Catalogues include detailed descriptions of each lot, along with accurate historical data, a reasonable estimate of what dollar amount the watch will most likely fetch, and superb photographs. I have accumulated quite a few auction catalogues in recent years and I've found them to be extremely useful horological references.
A forum is the perfect way to communicate with fellow collectors, whether you want to share a new acquisition with others or if you'd just like to chat about watches in general. The Rolex Forum is definitely one of my faves, as well as Timezone and the Omega Forum. I also am a member of some overseas forums, such as Orologi & Passioni. The absolute greatest aspect of watch forums is that the majority of them are of no charge to join.
Look It Up
Let's say you bought two Rolex Maxi dial Milsubs (pictured above) without actually knowing how valuable and uncommon these watches are. First, remove the strap. Then, look between the lugs at the 12:00 position. Last, take the reference number (5513 for the aforementioned Milsubs) situated between these lugs and type it in on Google. And there you have it, past sales results galore! Not only will you find pricing, but also an abundance of insight from various sources.
Thank you, Matt, for your question. Good luck in your horological pursuits and I wish you only the best!