Practice makes perfect.

Russian, which I am learning, has some challenges for English speakers in the way the pronunciation of vowel and consonant sounds can vary depending on their position in the word (stressed/unstressed/last letter of word etc.). Learn the rules for English by heart and keep practising them. Here is a link for Russian speakers on how to avoid mistakes: http://www.overcomethebarrier.com/2013/09/28/most-common-pronunciation-mistakes/

Being crazy to talk with native speakers and listen to local news, will help you forget all your incorrect accents dramatically.

Listen to English being spoken. English films and television if they are available, or DVDs with subtitles. Best of all, visit a country where English is spoken. If you can hear BBC radio, it is a good source of spoken English, but complicated.