Now I want to prevent this APK file from being reverse engineered.

抱歉,这是不可能的.

If it is possible to secure my app from reverse engineering,what are the steps to follow in my coding or any library is used for that?

正确配置的ProGuard将对代码进行模糊处理. DexGuard是ProGuard的商业扩展版本,可能会有所帮助.但是,您的代码仍然可以转换为smali,具有逆向工程经验的开发人员将能够从该smali代码中了解您的操作.

如果您不希望其他人看到您的代码,请不要将该代码存储在他们的设备上.