What is the best strategy for Coppersmith in Dominion?
You are correct in your assessment that in most Kingdoms, Coppersmith is a poor card and you would be better off with something else or just Silver. It has a couple of problems, as you have seen. It's terminal, so it doesn't play well with basic drawing cards that could give you a hand full of Copper, like say Smithy. It doesn't provide a +Buy, so if you do manage to pull off some combo that lets you play it with a hand full of Copper, you'll need to add yet another piece to actually use your money. And assembling a powerful combo is difficult since you need to not trash your Copper or even discard it to, say, Warehouse.

That said, Coppersmith's best friend is probably Tactician. Tactician provides big hands with plenty of Copper, another Action to play with, and that critical +Buy that lets you actually do something with all of your money. 

As Paul Marshall's answer hints at, a T1/T2 Coppersmith is fairly likely to connect with three Coppers and provide a T3/T4 Gold. That can help you get off to a good start, but then you have this increasingly-useless card in your deck. The presence of trash-for-benefit cards like Remodel, Apprentice, or Upgrade can make this kind of Coppersmith opening more attractive.

The Dominion Strategy Wiki has some more discussion. It also suggests that Coppersmith can be a boon to a very powerful draw engine that doesn't need to trash. Some combination of Wharf or Council Room (draw and +Buy) and King's Court or Throne Room (to magnify the power of the drawing) might make you take notice.