I'm going to address other factors not just "overpopulation" because that isn't the only problem, nor really the main cause of the problems the the world is facing in regard to this. To find a solution to a problem such as overpopulation, you really need to be aware of the causes, why are we experiencing overpopulation? Most people automatically think that it's due to having too many children, and don't realise there's other massive factors, like the decline in death rate - such a massive proportion of the population are elderly (60+), this is something we caused, due to advanced in medical care and suchlike, we can#t exactly go back on it now.
Space: Build ALL houses upwards, housing is a big problem, especially in the west where most people are greedy and want a nice reasonably sized house with a garden, but if all living areas were multi-story apartment buildings with hundreds of floors, you'd get 200+ houses in the space of 2.
Food: Distribution of food and other resources, we have way more than enough food on earth to adequately feed everyone, so that nobody goes hungry or starves to death due to lack of food, however, the distribution of said food is a massive problem, again mainly due to the greedy west. Also, less meat and dairy consumption would be a good thing as the amount of food and water that goes into feeding animals for people to consume could feed everyone in the world, but instead the animal goes to feeding a few.
Education: This is mainly an issue in less developed countries, but not exclusively. In many countries the job for a woman is simply to get married and have children, and starting this at such a young age leads to many, many children in that woman's life, we really need to do more than what we're currently doing to bring education to countries that don't have it. If a girl is educated, she will learn that getting married and having children young isn't her only option, there's other options for women.
I would also like to say that a one child policy is NOT a good idea, not at all. China abolished their policy for a reason, in attempt to lower the number of female infanticide (killing of female babies). While it did lower the number of children born, it also led to a significant gender gap as well as other problems. When the one child policy was implemented in China, many couples valued male babies over female ones, this led to many unwanted baby girls, and since only one child was allowed, the fate of these female babies often wasn't a good one, with orphanages becoming way overrun and filled with baby girls, others wouldn't have even made it to an orphanage. Is this really something we want to be advocating? I'm not denying that it worked to some extent, but the negatives out-weigh the positives to me. Not only that but policing what someone can do with their body to such an extent really doesn't sit well with me at all, there has to be better options.
I could say so much more on this topic, but there's no point in me blabbing on anymore.