As in every language, English speakers often revert to slang and cliches. Don't be afraid to ask what these mean, by understanding these phrases you will be that much closer to fluency and on your way to being able to speak correct English.
Most importantly, remember that all the listening and reading in the world will not make you a better speaker. Many people are intimidated at first when they try to jump into conversation, but it is the only way to improve your fluency and speak fluent English. Don't be afraid! People will be more impressed at your ability to speak a second language than your accent or mispronunciation of words.
Use any resources you can to better your English language skills. Doing research online and in your local library will help to strengthen your fluency, but nothing is better than getting out into the world and putting all you have learned to good use!