The way I go about is that I make a 4 bar loop of drums, bass and some melody or lead sound perhaps (This does most of the time turn out as the "drop"). Just to get the basic ideas off my head and into the project. Then I use the sounds I had in my little loop to make an intro or another part of the track. And this way you don't turn out with any drastic switch of the "sound" of the tune you are working on. I remember when I started making music and always begun with the intro, the drop always seamed so weird.
I guess the most logic thing is to start from the beginning of a tune when you are starting to learn it all. ^^