Watch films in Telugu with Bengali subtitles, or vice versa. This will expose you to the written and spoken forms of Bengali, and help you begin to understand Bengali words you understand in Telugu.
Translate words using a Bengali-Telugu dictionary or online translation resources.
Find a tutor or speaker of both languages who can help you learn Bengali based on your existing knowledge of Telugu.
Write out the Bengali and Telugu alphabets side by side to learn how they compare and to practice memorizing the Bengali alphabet, which is the first step toward mastering any foreign tongue.