The rental company will probably be able to provide you with advice when choosing a size, determined by the form of project you are involving yourself in.
Check out exactly what the site has in store with regards to rates and also you could always request for a free quote along with a demo too.
If you don't know what size to decide on, ask help through the dumpster company. Once a bin has been taken out of a site, it's taken to your MRF (materials recovery facility).
There is a large quantity of general trash from your job site that must be hauled away regularly.