• Using Mnemonics to link words - English: grumpy - French: grognon - a grumpy man groaning with irritation.
• The Town Language Mnemonic - To use the technique, choose a town that you are very familiar with. Use objects within that place as the cues to recall the images that link to foreign words.
• The hundred most common words - Tony Buzan, in his book ‘Using your Memory’, points out that just 100 words comprise 50% of all words used in conversation in a language. Learning this core 100 words gets you a long way towards being able to speak in that language, albeit at a basic level.

• Listening – You hear the word and you instantly understand it.
• Reading – You see the word and you instantly know its meaning.
• Speaking – You can use the word correctly for communication.

• Memory – You don't need to be able to remember the word when you want to use it.
• History – You don't need to know the history of the word or where it came from.
• Writing – You don't need to remember how to write the word.

"Sometimes Kenneth Hale was asked how long it would take him to learn a new language. He thought ten or 15 minutes would be enough to pick up the essentials if he were listening to a native speaker. After that he could probably converse; obviously not fluently, but enough to make himself understood. To those whose education, however admirable in other respects, had provided only rudimentary language skills, Mr Hale seemed a marvel.

And so he was. He had a gift. But he was also an academic, a teacher of linguistics at the Massachusetts Institute of Technology (MIT). He was aware that many otherwise clever people are dunces at learning a second language. He sought to find laws and structures that could be applied to all languages. As well as studying the common languages, French, Spanish and so on, the search took him into many linguistic byways, to the languages of native Americans and Australian aborigines and the Celtic fringes of Europe. As many of these languages had no written grammar or vocabulary, and indeed were spoken by few people, Mr Hale picked them up orally. His tip for anyone who pressed him for advice on learning a language was to talk to a native speaker. Start with parts of the body, he said, then common objects. After learning the nouns, you can start to make sentences and get attuned to the sounds. Still, there was much more to language than that."

Click here to read more on the Economist

Keith over at muscle.vox.com found a great article about how children learn a second language.  Here are the highlights:  

MYTH 1:
CHILDREN LEARN SECOND LANGUAGES QUICKLY AND EASILY

The requirements to communicate as a child are quite different from the requirements to communicate as an adult. The child's constructions are shorter and simpler, and vocabulary is relatively small when compared with what is necessary for adults to speak at the same level of competence in a second language as they do in their first language. The child does not have to learn as much as an adult to achieve competence in communicating. Hence there is the illusion that the child learns more quickly than the adult, whereas when controlled research is conducted, in both formal and informal learning situations, results typically indicate that adult (and adolescent) learners perform better than young children.

MYTH 2:
THE YOUNGER THE CHILD, THE MORE SKILLED IN ACQUIRING A SECOND LANGUAGE

The research suggests that younger children do not necessarily have an advantage over older children and, because of their cognitive and experiential limitations when compared to older children, are actually at a disadvantage in how quickly they learn a second language--other things being equal.

MYTH 3:
THE MORE TIME STUDENTS SPEND IN A SECOND LANGUAGE CONTEXT, THE QUICKER THEY LEARN THE LANGUAGE

Over the length of the program, children in bilingual classes, where there is exposure to the home language and to English, have been found to acquire English language skills equivalent to those acquired by children who have been in English-only programs.

MYTH 4:
CHILDREN HAVE ACQUIRED A SECOND LANGUAGE ONCE THEY CAN SPEAK IT

The Canadian educator, Jim Cummins (1980a), cited research evidence from a study of 1,210 immigrant children in Canada indicating that it takes these children much longer (approximately five to seven years) to master the disembedded cognitive language skills required for the regular English curriculum than to master oral communicative skills. Cummins and others speak of the "linguistic facade,"whereby children appear to be fluent in a language because of their oral skills but have not mastered the more disembedded and decontextualized aspects of the language.

MYTH 5:
ALL CHILDREN LEARN A SECOND LANGUAGE IN THE SAME WAY