For me, melody is the soul of a song. It comes first and matters most.
Anyone can learn orchestration from Adler, or study arranging in school, but a melody is a precious, heaven-sent thing.
Some composers write religiously at the same time every day. Not me. I can't compose unless I'm inspired.
Occasionally I'll feel an overwhelming desire to write late at night or at some other inconvenient time. I've learned to pay attention to that feeling, to drop whatever I'm doing and "strike while the iron is hot."
I write most prolifically when traveling, so you might say that many of my compositions are inspired by my travels.
Usually a melody will come to me and I'll sing it to myself, allowing the theme to evolve and develop organically in my mind. Eventually harmony, counterpoint and other formal elements will begin to suggest themselves. That's when I sit down and take out my score paper.