Walking on Stars

I've recently been working on an orchestra piece, and here is the finished product (first draft, at least). I know some of the transitions could be smoother, and I need to add most of the brass parts still. Any advice?

https://musescore.com/randomperson555/stars

Your harp player is going to have gripes. Normally the distance between one finger in a moving line to the next is a fourth maximum. The pedal work is sometimes awkward especially when you're trying to modulate... there's no real chromatic function that's easy to get to from a diatonic place on the harp.
I do somewhat question your starting off with a measure of silence, especially when it's gone and done so quickly, but it's not like it's that unusual. I just found it weird since it's over so fast.
I don't think you really used you bass or your viola? Why are they there? Just in case you want to add something later? I don't know musescore well so I don't know how hard it is to add instruments.
I think you take away from the energy of the moving line a little bit and the overall phrase when you don't let an instrument finish the phrase or line you've been working on, i.e. violin at m. 12 or cello at m. 18. This technique is really good when there's a dropoff you intentionally want to create, but I don't get the impression you want to do this most of the time.
I think you should take advantage of the ensemble a little bit more too. It's kind of sparse, especially in the big parts too which is a bit strange. You can add subtleties without changing the mood of the section, but I understand if you wanted something different... a lot of it felt uneasy to me.
It's a good draft. I think transition work would really help it along. 

Definitely good comments from @Monarcheon about the development of your piece. I'm going to focus mostly on notation because I don't have anything to say that hasn't been said!

- About the harp, notating it on two staves will help. The bottom staff should be left hand and the upper staff should be right hand, like a piano. You'll need to change the bottom staff to treble clef for most of it.

- bar 1, why have a blank bar? Were you planning to use it? If not, cut it out. If you want a pause of silence before you begin, just notate that in with instructions rather than an empty bar.

- bar 2 & 3, why write it in 8/4? 4/4 would accomplish the same thing and would probably be more effective for the conductor/composer. As a general idea, keep things consistent whenever you can, don't change without reason and make sure that reason is clear to the performers.

- bar 13 & 14, the piano part is funky. Change the voice or stem direction so the notes and flags don't crash! Also make sure your "objects" aren't colliding in general, there are some dynamic markings and such that collide with each other and with the notes.

- Measure 26, be aware of the inconsistent fermattas and the measure of rest in the cello. Check for consistency of writing.

The details can be tedious, but keep plugging away at it each time you write and pretty soon these things will become natural good habits for you!

Keep writing!

Gustav Johnson

I was going to say some things; however, @Monarcheon and @Gustav Johnson already said it.

This is still a good start but with the aforementioned advice, it'll get better!