1. Reference! There are tons of people who have thought up tons of ideas that you can use for inspiration. Pick one or two songs that you love that fit within the genre of the song you're trying to make. Pull them into your project and use them as guidelines for anything you feel unsure about. Arrangement, FX, orchestration, even mixing (ESPECIALLY mixing).

2. Get as close to a finished song arrangement as possible. Take everything you have and duplicate it out to your desired song length. Mark off the different sections of your song, and ask yourself what sounds would not be in the various sections. Delete whatever's unneeded, and you'll start to see how the track is supposed to flow.

3. Render the song out as a WAV file and load it on your phone. Get out of your studio or away from your computer or just out of the house in general. Change your location, and bring a pencil and notepad with you. Go sit down and listen to your track. Write down three ideas that come to mind for you to try, and estimate how long it will take to complete those ideas. They don't all have to work, you're just trying them out. Set a deadline for the song to be completed, and a deadline for the next session - using the time frame from your ideas as a reference. Shut out ALL distractions, and get to work.

Aside from the standard "subtractive" method of arrangement in which you just mute instruments and slowly add them in, keeping at least one element constant from the previous section makes transitions much smoother. It also allows you to add new instruments instead of just muting some and keeping the same instrumentation.