first of all decide that what kind of accent you want to have, bcz here are different different accent, like British,american, europiun, Australian all have different different, then after deciding this, watch their movies and TV channels, and try to make friends from that country for talking to them, it surly will help you to make accent

The following site has a person say aloud the words or sentence that you have typed in. Choose the accent that you like after you type in your word/sentence. http://www.oddcast.com/home/demos/tts/tts_example.php?sitepal