If its a bad day and I should happen to catch my reflection in a mirror purely by accident (for I try to avoid them at all costs on my worst days) I always give myself a little fright. I wonder who the grey skinned, dark dead-like eyes, palid complexion and very sad mouth belongs to. Its so sad really. So, I do try to avoid looking if possible.
But on good days.. I tend to become a little vain and look a bit more often. It helps to make up for the bad days views

I do wish there were more days like that.
I do try a little trick out now though, and it helps a little on some days. I decided I looked particularly ugly on one of my bad days a while ago, so I took a photo of myself looking bad and sticking my tongue out. (I think the view is even up my nostrils a bit... grose I know.) I even named it "Butt Ugly". Now, when I get a "down day" and Im feeling grose about myself, I pull out "Butt Ugly" and do a comparison. And most of the time, I actually look at it and think - "yeah, you know what, I dont look too bad today after all".
Sounds daft but give it a go... It might work a little for you too!