Write stuff as the need arises, typical, one set out an idea, usualy a lyrical with basic melody, two record what is there, three play back and evaluate=redoing mostly the whole thing, four rerecord/arrange etc. Done. I never have any problem with tunes since the popular taste is very predictable unlike some other song writers I know. They overwork the tunes and the result is tiresome sounding like bad jazz or worse yet apeLennon/anypopband. A bad ORIGINAL tune is far better than a good clone!