Select your most commonly used idioms and phrases in your native language and write these down.
Translate these idioms and phrases colloquially. Don't just go to a dictionary and translate it word for word -- idiomatic phrases rarely translate easily with a dictionary. Ask a native speaker or find a slang dictionary in that language.
Memorize the translated phrase and use it as often as you can. If you have regular contact with native speakers of your target language, try it out on them. Your friends will teach you new phrases as well.
Don't worry about correct grammar and usage just yet. Simply allow yourself to acquire as many words and phrases through exposure as you can from the contact with native speakers.
Sing songs in the target language. There is no better way to acquire new vocabulary than song. Learn a song in your target language and write out the words so you can visualize them as you sing.
Once you have acquired about 200 words you will be able to hold a rudimentary conversation in the target language.