Paul is absolutely right. English is a CRAZY language, and practice is very best thing you can do to improve.
A few further tips:
1. Focus on simple sentence structures: You'll learn more complicated sentence structures as the grammar becomes more natural to you. Focus on getting the basics right, and then build from there.
2. Vocabulary, vocabulary, vocabulary: Native English speakers value a bigger vocabulary more than mastery of advanced grammar.
3. Slow down!: Speak slower than native speakers. When you speak quickly, the beginnings and endings of words tend to blend together, making it more difficult to understand the words that you are saying. When you slow down and speak clearly, the listener can focus on your words.
If people can understand the words, then your native accent won't matter. People might even compliment you on your lovely accent!
English is challenging, but so much fun! Always remember to have a good time and don't be afraid to make mistakes. I'm a native speaker, and I'm still learning the language. English is always changing, so nobody ever really becomes an 'expert'. We're all in this together!