Let's see... First of all, i find it help me to start writing down something in the arrangement view to start the creativity. Obviously first i prepare some elements that work togheter, to have something to arrange
Give you a time limit, let'say two hours, to prepare some basic loops. After this start to arrange them, even in a cheesy way. Not writing down anything it's worse than writing down something cheesy, because there is the risk of being stuck in loop mode.
Usually i like to start create the main verse loop, and start arranging with it full force. I copy it for a number of bar and then delete the parts i feel are not needed in the intro. Here the magic happens, when you have your 16-32 bar section, start creating something else that will fit in that section. For example in the intro it could be a percussive workout. I program 2-4 bar of this, then i turn off quantize and start positioning it in the arrangement once i find a spot where it sounds good. From there i keep those bars looped and continue to program notes in real time where the music need them.
At this point, if the idea that come out need the usual 32 bar, well, fine... But if i feel it can go on, or better it has to go on to reach it's completion, i continue to write, could be i end with 34 bar, 40, 38, etc etc.
I find it helpfull not thiking in term of classic sections, intro chorus verse etc, but to think of the songs as a complex interaction of elements, in wich every element lead to another. In the case we were speaking, think as the percussive workout not as the intro, but as a musical idea that lead to something else. So maybe it could go on from last 5 bar of the intro to the first seven of the first verse, and there serve as a bridge to start something else.
Also,when im stuck with the arrangement i find that manipulating my current sound give me other elements and idea to work with. In the song im working now i thought there was the need of a tribal section. I took a loop, putted it in a sampler and messed with it, transposing, filtering, delaying, chopping it, and then resampling... And from a sample library loop i now have 5-6 percussive elements that are totally different from the initial loop and kick started my creativity.
Resampling a section of your song is in my opinion usefull to keep having variations and elements to work with, that in the end wont feel disconnected from the rest of the song.
If i remeber well, i read a topic where you asked if synth are important.. I read about synths, and in the end i use them, but i definitely use samplers and resampling techniques more. Try it
Hope this help!