The way most recycling works, is the "cleaner" the bundled recycling, post sort, the better the chance somebody will buy it. Capturing Aluminum basically pays for everything else in the recycling process, especially since the Chinese no longer accept cardboard and paper. So the price of the recaptured aluminum, to some degree, subsidizes everything else.
With Plastics, only 1 & 2 are widely recycled (occasionally 5). so the first thing you want to do is never, ever, bother with 3,4, 6 or 7 (and probably 5). Just don't. Throw that shit away. If the container isn't clearly marked, throw it away. Separate the caps and toss them. Mixed materials are largely not recyclable. Basically the more hourly workers have to hand sort that shit, likely the more expensive it is and the less somebody will want the post sort bale. Which means the landfill.
Plastic bags are the fucking worse. The absolutely gum up the machines in most facilities. Never, ever, ever, ever leave plastic bags in your single stream. Unless your community tells you to. Most grocery stores will accept your bags. But I encourage folks to get reusable bags and use them. Everytime.