there sometimes are settings in your synth that allow your lfo to restart when you play a new note, otherwise the lfo will continue to oscillate throughout your song without restarting this is most likely the problem.

One of my biggest arrangement tips is to drop your favorite tracks into your DAW and map out where things happen so you can copy the structure. I think this has helped me more than any youtube tutorial/music lesson.

In regards to adding in atmosphere, if your using Ableton you can use the resonator audio effect to tune an atmospheric recording to a certain key that way it sits in your song better... but Im guessing your using fl studio.

I think your lfo might be out of sync, at some points it seems like its not doing a full cycle before repeating. Also I would try messing around with adding in new types of bass sounds and switching between the bass noise you have  and some new sounds, which could give this song some phrasing/verses. Mix sounds pretty clean, and I really like the weird background effects. Was that just a sample or did you use a synth?

Pretty clean mixdown so far. One thing that stood out to me were the vocal chops, they don't feel like they fit this song to me. Maybe you could replace them with a pluck style synth patch or something else, the actually notes the vocal chops play are great. Just thought maybe you could try swapping them out with something else.

just an opinion so please take it with a grain of salt. 

-deño

Your arrangement is great! Everything flows really well.

One trivial thing that took me a long to figure out in serum was how sometimes when modulating a parameter with an lfo, the lfo would modulate on both sides of the center point of the knob and sometimes it would begin on the center. To toggle this setting open up the modulation matrix and click on the arrows that point like this <-> and it will change to this -> and vice versa. Super trivial but also really annoying.

Another really great thing serum can do is resynthesis where you can import a sound and serum will create a wavetable based on it. The best way I've found to import a sound from another synth is to bounce an instance of the noise you want to import to audio tuned to F#0 and -22 cents, and drop it into the 2048 tab on an oscillator. It goes over this method in the user manual. This can really open up endless possibilities.

-deño