when im chopping up pieces of my samples im keeping in mind intros, bridges, chorus, verses. arrangement always changes for me, but i like to do a few bar intro, 16 or 8 bar verse, 1 bar bridge, 8 bar chorus, back the verse, sometimes i throw in little 1 bar changes to make things less repetitive, outros. a lot of the time im chopping something up too much to be recognized as anything else, so if there were a melody in the sample, its gone now. if i need to add basslines or if im trying to tune my kicks or add some pads or something ill try to figure out what key everything is being played in and add stuff accordingly.
sometimes im not using samples, and if thats the case then im writing everything with a certain scale or key in mind. im also at all times thinking about filling up the spectrum nicely and trying not to have any area too crowded.
just keep making songs, your arrangement skills will get better and more complex.