There's not much I can do to my house as I don't own it, but my housing association started taking measures to improve energy efficiency a good few years ago. Re-doing the cavity wall and loft insulation was the first step, followed by new double-glazing. The next step was to install solar thermal panels on the roof, a measure that had an instant effect on the electricity bill. A year or so later, they installed a new heating system with an air-source heat pump; this further reduced the energy bill. Most of the lights in the house are on low-energy bulbs, apart from the fluorescent light in the kitchen and one single incandescent bulb in a cupboard that only gets used for a few seconds at a time; the former is on its way out and will be replaced soon, while the latter will be replaced when it decides to blow (I'm not chucking out a perfectly good bulb when it's rarely used).
As for my diet, I'm still a meat-eater, but I do eat far less of it than I used to, and have done over the last 20 years or so. Having previously shared a house with a vegetarian and two vegans, I found it quite easy to adapt meals that I would normally make with meat such as mince, first by using Quorn mince or similar. More recently, I have been experimenting with different lentils as a substitute. Having said that, nothing beats a big plateful of mince'n'tatties!