Picture of Vintage Knitting Pattern Tips and Tricks
For a truly authentic vintage knitwear look, you just cannot beat a vintage pattern.  And there are hundreds of these patterns available online for free!  A quick search in the Ravelry database, or even Google will yield an amazing number of gorgeous possibilities.

[The pattern for this particular sweater may be found here.]

Step 1: Terminology

Picture of Terminology
One thing to keep in mind is terminology.  For instance, substitute "jumper" for "sweater" in a google search, and British vintage patterns will jump to the top of the list.

Other words that will help to narrow a search are cardigan, crew-neck, pullover, lace, bolero, and shrug.