Where to find proven design patterns?

A good place to start would be the Reference Design Library at AllAboutCircuits.com

It has a large searchable database of common circuits.

Another option is more vendor specific. For instance Texas Instruments has nice tools for helping design typical circuits.

Even Digi-Key has a good reference library.

If you are looking for more basic/fundamental circuits, I think you would be best off with a book such as The Art of Electronics.

Most (all?) chip manufacturers publish application notes showing how their chips can be used in a circuit, and these usually contain reference designs that you can use.

How well these designs are tested varies from manufacturer to manufacturer and probably even depending on which applications engineer wrote the note.

Historically there were books that collected these designs, mostly copied directly out of the app notes, with titles like "1001 Electronic Circuits" or "501 Measurement Circuits". But those are hardly needed in the era of Google.

Art of Electronics is good, the other sources mentioned in other answers probably as well, but I just have a nagging feeling that there's an underlying assumption at play here, which is false.

At the risk of being blunt, I dare suggest that there is no "smarter" method of developing electronic circuits, and no way to cut corners. Trying to save design time and effort will cause even more delays at a later stage in design

The analogies between software development and hardware development are not exactly one to one. For example, in software development it may not be necessary to know the inner workings of something like a MPEG video decoding library, you just use the library. Similarly, in electronics, you don't need to design an MPEG decoder if you can pick that up as a component. But there the analogies end. In electronic design, the division beween what you design (your own circuits and printed circuit boards) and what you use (ICs that other people have designed) is quite clear. You cannot tinker with the IC design, unlike that MPEG decoder library, whose source code you can probably look.

In electronics, you design what you design and you must know completely how it works. You cannot, generally, just take one circuit from one book and another circuit from another book, throw them both on the same PCB and hope that they work together. I think you must have a complete understanding of how each of them works so that you can evaluate how they work together.

No way to cut corners. No way to work smarter, not harder. That's my point of view anyway. You don't need to reinvent the wheel - in fact, you absolutely must not. You better be well familiar with the design of the wheel even before you start designing your product, and then measure and re-measure it so that you're pretty darn sure that it's round before you ship it to your customers.