No drugs or alcohol before playing. I have a terrible memory when it comes to guitar stuff, usually I keep a notebook with chords/notes for songs on top of my amp or on the floor. If I start drinking, it becomes way too hard to concentrate on these things
I've always played in doom bands, so it's fairly obvious what I like to do when the mood strikes me.
Before I started drinking, I'd always down like half a bottle of Nyquil or Robitussin to take the edge off. Now, I have alcohol. And the world is a better place.