Renovating a property produces a lot of waste and consumes a lot of resources. There is simply no way around that. Hopefully your work is replacing something that no longer works and the new home is going to last some time. This is the first major renovation the flat has seen, so once every 40 years isn't so bad. That's what I tell myself anyway.
Still, it's good to limit your consumption where you can, and I'm a great believer of tiny accumulative efforts growing to great change, so all contributions help. Here are my tips on being conscious about your resource use when it comes to DIY.
Rather than buy a new rail for my wardrobe, I choose to paint the old one black. It looks great, and the paint cost me less than a new rail would have done. The shelves in the living room that I inherited with the flat are going to be rehung in the garage to provide some storage for my tools, when they no longer get to live in the flat full time! And the bath that I had taken out I sold on eBay to someone who is going to reuse it in their renovation.
The thing I love about reusing items is that I don't throw something away and I don't need to buy something new. That makes reuse a double whammy of less waste and less stuff, and why it's number 1 on my list. Plus there's nothing so satisfying as taking something kind of gross and making it into something beautiful and useful again.
The idea of repurposing is taking something that does one job, and using it as something else. Like breeze blocks as furniture. The only example I can think of in my own flat is the light from the bathroom: a milk glass globe shade that I've saved because I believe it has the potential to be a cool flower vase once I've designed/imagined/made a base for it.
This is similar to reuse but is for materials rather than objects, so it's got that same double benefit of not adding to landfill and saving resources (and you money).
The flooring in the living room will (eventually) be parquet block, which I got through freecycle from another house renovation. I've been using a fair amount of reclaimed paint and tools from Orinoco, and I've been sending the useable materials I don't need back to them too. The felt under my bedroom carpet was a left over roll that my parents had from relaying in their house last month (that was good timing), and itself was made of recycle wool fibre.
I've also been using scrap wood that comes out of the demolitions as materials to build new parts of the project: sometimes simply as a drilling base, or for hiding pipework ("boxing out") in the cupboards, and later I'll be building a "new" linen rack for the boiler cupboard from timber reclaimed from the old airing cupboard. And any wood that doesn't make it back into the flat has been going to my parents' shed for their wood burner this winter.
Simple idea, maximum impact: the less you (over) buy the less waste you're going to risk being left with at the other end. As was the case with my tiling, trying to keep the materials you do buy down to a minimum really helps reduce waste on a project. A word of warning though, this is surprisingly hard to achieve. With the tiling I ended up buying half a dozen tiles to finish the job rather than ordering a whole new box of 32, which although resource efficient was not the cheapest way to go about things.
Lots of building materials can be recycled as long as they're not contaminated with other elements, so proper waste separation is really (dull but) important. Glass is a well known recyclable, but plasterboard, timber (which with my local council includes chipboard, mdf and hardboard) and even masonry rubble can be recycled if properly disposed of. Most local councils have a waste facility where each of these materials will be taken.
So there you have it. With a little organisation you can keep your waste down (and sometimes your costs too) and help keep the world beautiful while you make your little corner of it a whole lot better.