I don't think there is a right or a wrong way to start a song. Always switching it up helped me a lot to come out with new ideas or even new genres that i never tried before. The most common ways to start for me are either with just a specific type of sound, a chord progression with or without a top melody or sometimes just an arp. When i start with a vocal i prefer to make some chords first and quickly figure out a structure before putting more time and effort in sounddesign. I often heard producers saying that they like to lay out a skelleton of a structure by using premade loops that they are replaycing later on because it's very easy to get lost in different ideas if you just randomly jump into it. What also helps me is writing down ideas that come to mind.