The storyline that you should follow:
1) Black Butler Season 1 Episodes 1-15)
2) Ciel in Wonderland part 1 & 2
3) Welcome to Phantomhives
4) Book of Circus
5) Book of Murder (parts 1&2)
6) Book of the Atlantic
7) The Story of Will the Reaper
8) Public School Arc
9) Emerald Witch Arc
The above are the only ones that are canon or filler that will not take away from the overall story. The rest are OAV and not part of the manga. They are made up stories that complete the Anime, but since Crunchyroll has restarted the Amime I'd recommend not watching the ones below.
10) Black Butler Season 1 Episode 16-25
11) The Making of Black Butler II
12) Black Butler II
