I have been screwing with watches for over 40 years (20+ with replicas) and could not help but learn a thing or two.
A few are listed below in no particular order:
1...Look at every watch as it is, not as it could be.
2...After estimating a repair or project, double it just to be safe.
3...Stay away from expensive brands that do not sell parts.
4...Do not assume a genuine rolex movement is any 'better' than a fresh Eta in a project watch.
5...Keep at least 330 feet (100M) away from all AD except to window shop.
6...Never buy a new watch for list price when hundreds of good used examples are available for half price. They are all used after you wear them.
7...Always take "It has just been serviced" with a huge grain of salt.
8...There is no such thing as a 'Grail Watch". Think of them as potential ex-wives to put them in perspective.
9...Quartz beats mechanical hands down (especially chronographs) but they are just not as 'cool'.
10...Never believe a depth rating.
11...If a watch fogs up, it is usually from a leak, not a change of temperature.
12...All watches look better on someone else's wrist.
13...Never artificially 'age' a watch if you plan to ever sell it.
14...The more expensive a watch is, the more fragile it usually is, and the more expensive it will be to repair (Patek, AP, VC etc come to mind).
15...Any 'project' replica watch is only worth the sum of the parts no matter how much it cost to put together.
16...I have 15 or 20 dials that I got from 'Paul' with Singer perfectly stamped on the back. Does anyone doubt they are genuine? Nooooooooooooooo.
17..."An etaclone is just as good as a genuine Eta." Sellita maybe, but not the Chinese ones.
18 "Swiss Made" my azz. A large percentage of 'swiss made' watches are 90% Chinese by volume and 51% swiss by cost.
19...The Seiko Kinetic and others like it are the answer to a question not asked. Who needs an automatic quartz watch?
20...Hairsprings are the bane of the universe.
Etc, etc.
Note:
Number 6 helps to qualify number 5.