[Kanji_The_Wanderer]

It depends really. A lot of mangas the art reflects the story, and vice versa.

For example. A manga depicting a girl with giant green eyes and pig tails is probably involved in some sort of cute Shoujo manga that may be based on love and romance.

While a manga with an in-shape guy with a tattoo and a sword will most likely be seen in a bloody/action story.

So firstly you should decide what types of characters you are interested in drawing. Everyone has limits and preferences. So it might be easier for you to draw a cute school girl character who will probably have a much simpler character design opposed to a stern looking buff guy.

I recommend that you give it some thought before you pick a genre.