I've been extremely lucky over the last six years in that I have gig that is basically writing and producing original songs for educational curriculum. I mention that because I wanted to point out that I have to come up with a lot of music and hit specific deadlines. This year I have four specific deadlines and have to come up with 22 songs that deal with specific subjects. The people in charge of building curriculums give me a list of the subjects to be covered (with a short description) and that is all I have to go on.
After working this way for so long, I've come to the belief that the single most important thing you need to figure out is your subject. More specifically the title, even if it's just an instrumental piece. Because I am given a specific subject, I don't have to dwell on the titles as my song titles tend to be variations on the subject.
Two that I am currently working on are "Dulcimer Song" and "Music Helps You Study," which are basically the titles for those two lessons. The Dulcimer lesson called for a musical piece to allow the student to hear what a dulcimer sounds like, so that meant the song had to be based around an actual dulcimer. So drums/percussion were out, as they would overpower the featured instrument.
I find it's easier to sit words on top of music, much like scoring any other melody instrument. Therefore, I first came up with some chord patterns based on an actual dulcimer. I found an excellent sample-based dulcimer for only $30.00 from the good people at Indiginus. It's for contact and I was able to come up with an interesting chord pattern and a hook by playing around with it for a few hours.
Next, I built the various patterns and hooks into a structured piece of music. I am constrained by a child's short attentions span
so I rarely go beyond 2 minutes for a song.
The song subject dictated that it would be an acoustic piece with a basic Appalachian/backwoods type feel, so I built the arrangement accordingly. I also decided at this point that I would be casting the song for a female voice, which dictated where the key would go and gave me some boundaries on how wide the melody would range. I have a half hour commute to work each way, so after I get a basic demo down for a song or two, I make a CD and just play it over and over for a couple days. I start singing along with it in my head. Sometimes a bit of a lyric will start to emerge. At this point I was mainly interested in something to go along with the hook I'd developed. Once I had that I started writing words.
The title/subject also dictated the lyrical content. When I am writing a descriptive song, I research as much history/facts/etc. that I can and copy/paste it all into one doc. Then I start pulling out what I deem are the most pertinent bits of information and paste them into my lyric writing program. I use MasterWriter and it's the best investment you can ever make as a songwriter. I used to use the Clement Wood Rhyming Dictionary, which was awesome at the time, but MasterWriter is the most efficient way to put a lyric together. There are different options to license it and you can purchase it outright for under $200.00. There is also a free demo you can download. It combines a large rhyming dictionary that shows the words in columns, which makes it easier to find the rhymes you need. You just highlight the word you want to rhyme and bring up a list of all the possible rhymes. You can also get sound-alikes and phrases. You just click on each word/phrase and they are put into a list for you. To round that out there is a very good Thesaurus and Dictionary that work the same way. There is also a simple audio recorder that you can put your idea down on.
I apologize for going on and on about that product, but I honestly couldn't do my job without it. I think that regardless the style of music or type of lyric you want to write, this will simplify the process. It also puts everything into a convenient, searchable database and has an option to allow you to register your finished song. Enough about that.
I also apologize for the longwinded post, but I wanted to express what I feel is the most important thing about a song. Of course it isn't the only/best way to work, but for me it is a method that has consistently produced results.