The most obvious way to do this is by increasing the efficiency of our technology. We have to accept that the population of the world will grow (though we should try to reduce the growth rate) and that people will want more things (though we can try to moderate that as the first post argues). Therefore, what we must do is to provide the things they want more efficiently and with less damage to the environment. That means, for example, pursuing energy technology that is renewable and does not pollute. If we could develop such energy sources, we would be able to increase our standard of living without having to pollute too much while making the goods that people want.
This is a very big question and I am sure that many people will have a whole range of answers to give you. However, let me get started on my response first!
Now, this may not be a popular thing to say, but I do believe that there is proof that if we are serious about doing what you say, then we need to be honest with ourselves about the fact that on our planet today there are countries and groups of people that are using far more of their fair share of the world's resources than others, which is creating an unequal world. The facts are that developed countries such as the USA enjoys a quality of life that is much, much higher than your average citizen of Bangladesh, for example. However, at the same time, we need to recognise that there is only so much to go around for the world's citizens. Therefore what I would suggest is if we are serious about improving the quality of life of the poorest of the world's inhabitants, a great place to start would be by trying to make our own lives more simple and reducing the amount of the world's resources that we ourselves consume.
Whenever we think of quality of life, it is important to consider what you precisely are refering to. However, if we think about the quality of life for the average person in the USA, for example, they have all the basics in place: shelter, food, education etc. Whereas if we look at other poorer countries, they don't even have some of these. Therefore I think we in more developed nations can afford to reduce our consumption whilst still keeping those basics in place. This might mean taking very simple steps like buying local produce or growing our own vegetables or reducing the amount that we fly or drive.