The way to pronounce "often" is not "Of-TEN," but it is actually "of-fen".

Just think of "listen".

Do you pronouce it: "Lis-Ten?"
Then don't say "Of-Ten."

Many people pronounce the word often, "of-TEN" but they are wrong. 

The "t" is silent.

Just like "hasten," "soften," "moisten," or "glisten," you don't say the "t."