My in-head metering scheme with my M2 is very, very complex. But, now here for the first time I can share it with the world. I believe this method covers all the bases, and you're welcome to adapt it to your own situation:
I start with a guess. Now, many of you will accuse me of being half-assed, but I really am diligent. Listen: First, I subtract a stop for my bad eyes. Then, I add a stop and a half to protect the highlights, subtract a stop because it's expired film, subtract a stop because it's a hazy lens, add a stop to squeeze out some more depth of field, subtract a stop for luck, add a stop for love. Then I add a half a stop because the sun has gone down during my all my figuring. Of course, I subtract a stop because I'm not sure if my developer's fresh. Finally, I add one final stop to to amp up the mysterious drama. Then, and only then will I squeeze the shutter to allow just the right amount of light into the box.
I'm still looking for a meter that can handle these calculations reliably.