I know that's a pretty general question but really anything helps. I'm just beginning songwriting, and I've managed to get the hang of how to make a song sound like grindcore/goregrind, but as soon as I try to venture into deathcore I'm pretty abysmal. Any suggestions for tunings, etc? I use Finale Notepad 2012 and I find it hard to get the notes I want on guitar, so if anyone knows a better program that would help too. Thanks if you took the time to read this and thanks in advance if you offer some tips!

I reckon drop A is pretty common in deathcore.

To me it sounds like your premise for writing a song is a bit off. Shouldn't you be writing a good song, first and foremost, and let the genre be determined by what you're influenced by, and what elements are most appropriate for your song, and that particular project and band.

That's a good point, but I mean more in terms of when I make the transition from a riff in my head to putting it in the program, it doesn't sound accurate to what was in my head. And what I'm influenced by in this case is deathcore, thank you for the tips and insight man!

Writing deathcore is, largely in my opinion, all about transitions. I’m not really too familiar with technical terms, so I’ll try and explain this as best as I can.

A breakdown isn’t shit unless you have something built up behind it (a lot of tension and suspense). One can come at the beginning of the song provided it’s groovy enough, but for the most part the latter sentiment holds true. I’m not sure exactly how to articulate when and how a transition will make sense, but I know it has a lot to do with varying tempos/time signatures/rhythm patterns/rests while keeping something constant. For example d beat part > blast riff > pause for a measure > breakdown. Or keeping that same flow, but adding strictly bass guitar during that pause. The band that has mastered this art in my opinion is Dividing the Masses. Their riffs are elementary as fuck, but their music is so powerful and emotionally charged due to the weight of their transitions.

Simple: study arrangement! Doesn't matter what style of music you play, If you don't know arrangement, it will fall short, that was a mistake I committed when I began writing music. Start looking for the basics on song structure and how you can build tension within a song.

As for software, FInale is great for most scoring purposes but it's kinda crap when it comes to metal, on your case I would just stick with Guitar Pro, which is great for metal band arrangements (drums, bass, distorted guitars, etc) but it's really shit for writing anything else (trust me I tired writing an orchestral piece in Guitar Pro, caused me a lot of grief).