It's a good start.
The first thing I have to point out is that the 'two' anime don't correlate well. Also, neither fit with the song, in general. There were times when the clips matched the lyrics being said, but if you look at the song as a whole, they just don't work together. "Fireflies" didn't have any part in your video, which isn't that big of a deal, but it just felt random the whole time.
Next, it wasn't original. I'm not going to criticize the video because of that, but I'm just saying. This song has been edited to 504350943285834 times, and it's not even entertaining to watch anymore. I think there's been 3 releases with this song in the last few months. One of them was really good, and I suggest you do a little research before you start (if you care about whether your vid is original or not. Some just edit because they want to, without worrying about that thing, but if you look at it from the eyes of the viewer, it just gets boring.)
As for the actual editing, I don't really have much to say. At least it wasn't a bunch of long clips slapped on there.

But I can't help watching this video without thinking of Pozoroggo's amv and comparing the two. And when you compare the two, his is noticeably better, to be blunt. Sorry. I don't know if you care about the "competition" or not, but when people say "Oh, this reminds me of some other amv..." it's not
always the best thing. At least not to me. Which brings us back to the originality thing, but that's entirely up to you.
I also noticed you posted a comment on his thread of that amv. It honestly looks like you only got this idea after seeing his video, and it's good to draw inspiration from other videos, but to say "Hey, that vid is REALLY good, so I'm gunna use that exact song and do a 'mash-up' too" isn't cool, imo. But that's up to you.
Also, I'd suggest working on your quality issues, so when you add another video to the org, everyone can enjoy it via download and with good quality. The quality of the previews aren't always great, even if the quality of the download is superb. Just a heads up, because it's a good idea to have at least one good quality copy. Just read the guides and ask for help when you need it.
2/5 Keep working on it. Good for a second/first amv.