Don't know where to begin?

While ultimately it doesn't matter which arc you begin with, Cecil arc is recommended if you want my recommendation.

And then Masu arc + Shattered union arc. 

Feel free to visit the lore section as well which holds stories of its own.

Rocksea arc (4)

Set in Rocksea, the outskirts of Andromeda system, this arc deals with various characters who make their home in this region.

[Rocksea arc] [1] [Duchess' boobs] [9613]

Ehka had been a minor character that showed up in more than one story. Her first appearance is [Juron arc] [1] [The mad and the crazy] [9604]. Her career goes downhill afterwards. She also makes an appearance in [Ashuta arc] [5] [A date with the crazy] [9605]. You may notice a pattern here. And then her final appearance as a minor character is in [Milky way arc] [3] [Flawed system] [9613].

Now, she gets her own story as a main character. This is her reward, I suppose.

In order to fully understand what is going on, you need to read through a bunch of stories, especially the ones mentioned above.

[Rocksea arc] [2] [The Old Lady] [9620]

This is the real beginning of this arc. The previous story "Duchess' boobs" is a backstory to this.

[Rocksea arc] [3] [The fine line] [9620]

How would you define "an honest living"?

[Rocksea arc] [4] [Cracks] [9620]

Once you go <something>, you never go back.

Or something along that line.