a really cool trick is also making first the melody and then adding the base line (that would be to things like buried alive intro) and for arpeggios or that kind of stuff you can just jam to chords doing arpeggios until you find something you really like and a good thing would be knowing lot of chords to add more variety to your song and even make it better, also if you’re doing a jam and you find a progression like i don’t know C-G-F-G (I-V-IV-V of Cmaj) you can add notes in betwen the chords to make a voice conduction and that will have a really good impact on the progression and will improve the whole song or part you’re working on, and listen to a lot of music that have clean parts that you like and analyze them in a theorical way to see what’s going on and then try to apply it to your songs or clean parts