Libraries and book stores provide many resources, such as CDs and software designed specifically for accent reduction, to help your American accent. Resources with supporting visual aids will show you how to position your lips and tongue to get the sounds right. Visual aids also relate certain sounds with letter combinations. The best American English resources online use a combination of reading, listening and practicing speaking to learn the language and accent.
Enlist the help of native American English speakers. Friends or colleagues who are able to coach you during everyday conversations can provide valuable training. Tell people you welcome their feedback and value their suggestions. Ask them to specifically address any mispronunciations and incorrect word order when they hear those from you. Most native American speakers will feel flattered that you wish to have an accent like theirs.
If you are having trouble with a few sounds or pronouncing a few letters, then focus on one at a time. For example if you are a native Spanish speaker, you will tend to have most trouble with "j," "y" and "th" sounds. If you are a native Japanese speaker, you will tend to have most trouble with "v," "b" and "th." Find a particular word you often have trouble with, and include it in conversation throughout your day. Watch the movement of native speakers' mouths when they pronounce the word then mimic them. Practice on getting one of those sounds right instead of trying to master several at once.
Some of the world's largest broadcasting companies are American-based, such as NBC and CNN. Listening to news, movies and TV shows on these networks will help your American accent. Avoid British networks, such as the BBC, since their English pronunciation is different from American English. Only watch the American broadcasters to become more familiar with pronunciation. This will give you a good reference point for pronunciation of specific words.