The exact guidelines differ from place to place and depend on how the local recycling process is setup. Where I live for example, it's ok to leave metal caps on glass bottles because all metals are automatically filtered out, whereas in other countries people are asked to remove the caps. The same goes for plastic, some places recycle only specific plastic types and all plastics should be clean, and others collect all plastics and it isn't a problem if there are stains.
Generally speaking, it's best to separate the different types of material as much as possible (if they belong to different bins). For plastics it's best to leave as little food leftovers or other materials as possible because the more leftovers there are, the more the plastic quality goes down when it is recycled. Also biodegradable plastics are better not collected with regular plastics.
Bio-waste is generally everything that is organic and can be composted; food leftovers, grass clippings, egg shells, cardboard, paper handkerchiefs.
These are general guidelines. Your local recycling facility may have slightly different guidelines so it's best to check with them.