Not bad for a first attempt
For a first attempt at an orchesrated piece, this really isn't bad. Some things that you should work on in this pice are thus:
1. Though you had many diverse elements in the song, they did not seem to work together as they should. Except in very special instances, orchestral pieces tend to harmonize their sounds together. The beginning of the piece is quite good in this regard, but later, when the heavy snare drum comes in, the harmony starts to fall off.
2. A little heavy with the precussion. Throughout much of the song, the precussion tends to domanate all the other sounds. While this can be a good thing in some types of music, like military marches, in this piece, it seems to steal the attention away from the brass and woodwinds section. I think that the song would be a little more enjoyable if you cut back on the drums a tad.
3. The last thing is just a personal note. I find that orchestrated pieces are somewhat more enjoyable when you pick a certain type of instrument or a certain section to hold the lead through the whole song with the others working to support it.
Other than that, I would say that this is a good start, but that it needs a little more work to be perfect. Keep working on it and you will be great at this.