To me there's no real difference between how I approach soundtracks and other types of music. For this jam I just played around with silly compositions and sounds until I hit stuff I liked, really.. I've been putting a lot more effort into making music this past year and it helped me improve a lot. I will say though, I usually have a very hard time being inspired to create music. Essentially just coming up with stuff to create, and sticking with a project, is very challenging for me. Game jams like these usually give me that inspiration, since the game we're making provides context to the music.
Something that I felt always held me back was my limited set of samples to pick from. All of the percussion and some sfx in this soundtrack was pretty quickly laid out with samples from my sample library. I use FL Studio and they recently got a subscription system for samples (such as other similar services like Splice), and getting access to that allowed me to way more easily look for sounds to use in my tracks. Just having access to a huge library of high quality sounds helped me achieve a good foundation for the music, and it really boosted my creativity too I think. That said, my previous OST was made almost entirely using free instruments from spitfire, where I heavily focused on composition. So it just depends on the scenario I think. But even then, just high quality sounds and instruments in general helps a lot for how the song turns out.
Although I think for the most part I focused on the composition itself for these tracks too. I usually just pick or create some instrument and play around on my midi keyboard to find something interesting. Some of these tracks I didn't even have any plan going in - not even where in the game they'll be used lol. I just had fun! Others spawned from an initial idea, such as the beginning of Gogogo!.
I think composing interesting melodies and arrangements just comes from experience. A lot of the time when I put stuff down, it's either just intuition or landing on an instrument/melody/sound that I either think sounds good, or I just find funny. Most of the time you gotta just trust the process and play along. Make a lot of stuff and use other songs as references! I'm sure you'll get to a point you're happy with soon enough :) Good luck making music!!