Some good advice in here. One thing I'll add is: make sure you know which English words have weird spellings that are nothing like the pronunciation. (This is a lot of words!)

The huge mistake I hear non natives make all the time is to incorrectly pronounce things like they're spelled. Eg pronouncing the "b" in "debt" (it's actually pronounced just "det" in every dialect), or pronouncing "says" with the same vowel as "say" (it's actually more like "sez" in most accents.)

There are zillions of other examples - I can't give you a list of words to be aware of, but I'm sure that someone somewhere must have compiled a good list.