Speaking as a native of the United States, first and foremost, Do Not Worry! We have a large number of long term residents whose English is quite poor, yet they survive and even thrive. As Americans, most of us are quite used to a whole range of English proficiency and are not troubled by it. You will be treated well, and kindly, by the vast majority of Americans who readily understand that English is not your native tongue but also appreciate that you are learning and trying. For the few who may not treat you well, they are not worth your effort. In the meantime, I like Peachey's suggestion. Listen to and sing along with some simple songs. Read some passages out loud, especially some things that you might find on the Internet which have a recording that you can mimic. The most important thing is not your vocabulary or grammar, it will be the ability for others to understand your accent. In the end, do not panic, just try to enjoy the interactions and realize you will make mistakes. That is okay, it is how you learn! Bon voyage!

Is it just a visit? Don't panic about it too much. Yes, your English still needs a lot of work but I understood your question well enough. Speak it! Listen to songs and try to sing along. Repeat phrases you hear, as you watch movies and TV shows. Use the language. Keep paying attention and don't be afraid of mistakes. The learning never stops. :)

Writing and reading are more time consuming.I think listening is a better option, english channels,etc..and most importantly keep your dictionary handy..:-)

Hi this site gives you basic English travel phrases you will need http://www.learnenglishfeelgood.com/travelenglish/

Don't worry. When I've been to the US, I met people who knew just few English words, and they survived. I mean, your English is not so bad as you think (judging from the phrases you've written above). The American people are very friendly, and they got used to communicating with foreigners. Just don't be embarassed. I'm sure you knowledge of English is quite good for not being afraid to go to the US. (I know it from my own experience). But I agree with Nils that listening is the best option. My American landlord once told me about the boy who spoke English almost like a native speaker, and he learned it from movies. Well, good luck. I hope you'll enjoy the trip.