The researchers used the keyword method, a memory strategy by which a target item is memorised in relation to a similar sounding word. For example, to remember that carta means letter in Spanish, the word 'cart' could be used as a keyword. An image of a letter in cart is then imagined, allowing the learner to derive the meaning from the image (source: http://www.memory-key.com/mnemonics/keyword.htm).
In this study, speakers of English were given 120 Russian words to learn, and provided with the equivalent words in English. There were three groups: one made up their own keywords, one used keywords provided by the researchers, and the third was a control group who did not use the method.
It was found that experimental group did 50% better with immediate recall, and 75% better over the long-term (6 weeks) compared to the controls. Being provided with keywords led the better results.
It is notable that this method can only help with a limited aspect of language learning - the acquisition of vocabulary items which can translate directly into the learner's first language.
Atkinson, R.C., and Raugh, M.R. (1975). An application of the mnemonic keyword method to the acquisition of a Russian vocabulary. Journal of Experimental Psychology: Human Learning and Memory, 104, 126-133.