Well, it's not exactly a secret, but for enhancing speaking fluency I highly recommend "shadowing."

Find some audio (or video with sound, obviously) that is just slightly above your level.

You will probably need some text too. Ideally you can find a transcript, but you can also use subtitles in your target language.

Pause it after each phrase or sentence, and then repeat exactly what you just heard, imitating the speaker as best you can.

Important to repeat multiple times with the same material. The time between pauses will become longer and longer. Maybe someday you will be able to do this without subtitles! (I cant ... yet).

It's pretty hard to do, and (for me) tiring, but I find it extremely valuable.

Daily practice speaking it out, listening to audio clips/podcasts, composing a sentence or two about your day using the language, watching a film of the language and "mimicking". 

There are no "secrets".

My method is simple: consistent daily effort involving both input and output, using a variety of tools.

Oh, this "shadowing" is a really effective tool! I did it myself and found out that it amazingly helps to improve accent! And speaking in general, of course.

 By "secrets" I just meant those things, that make your progress faster :) As for me, it was listening to the podcasts and conversational practice.