Just my opinions and our styles may differ so I don't think my ideas are the ONLY ideas...
Upgrade your mask and hands. I have that mask cuz it was supercheap. I built two static props this year. One had a Death Studios Mask and it looked scary and awesome. The second one was one of these and looked so-so. It took me a while to figure out why until I realized the mask just looked like a mask. So now I try to use only high quality masks on props that are near the crowd or a focal point.
I mentioned Death Studios, but not sure they have a mask that would work for you...something like Ghost Ride Productions, Inc. might work for you though. They have hands too btw.
I assume you have electric buzzing sounds and a strobe light on this as well - if not, add that.
For the prop itself, I would change the band around the head to something more like a bowl shape. The strap around the neck looks metal too - a leather strap might be a better touch - an old belt would work probably.
The chair itself looks a little too "fresh" I would distress it a little myself.
I think the body form looks pretty good - seems well proportioned. Just my opinions for improvement - I think it looks pretty good though overall.
You can use a couple straps to hold the legs to the chair, a dome type fitting for the head, I throw switch for the electrical power, a couple flashing lights. Power pack or transformer to run wires to the chair so people know where the power is coming from. Looks good overall. The chair might get lost in the dark since it is dark itself. Way to go though, I know an electric chair can be a pain to make.