Getting down to why you write. If you're trying to write a "hit" then Foe is probably right on the money. I took a book out of the library once, out of curiosity. It had a sure-fire way to right hits. The first suggestion sas that every time you think of a cliche, write it down on an index card and file it away. If you can write a song with a cliche as a title, you've already got some recognition... "Double Or Nothing," "Between A Rock And A Hard Place" (that one's already been taken by the Stones,) etc. If you want to reduce life to cliches, that's the way to go. That's not why I write. I don't write to make money or have hits, and in that regard I've been a whopping success! I write them because I enjoy writing them, and when someone else enjoys something I've written, that's payment enough.
As to ways to write songs, we all have our own. I have probably written at least three songs in my life, with instrument in hand. All the rest I "write" in my head. It's not until I have the song well-started with the melody in place that I pick up an instrument. Many of the songs I've written have come to me when I'm driving, so it's just as well that I'm not trying to play guitar at the same time. That's what works for me. Doesn't work for most people. Whatever works. There is no wrong way to write a song.