The plastic or paper bag helps a little bit and putting them in direct sun does help ripen some vegetables like tomato. Ripening avocados or any fruit/vegetable just takes time and patience.
Ive always been told to ripen any fruit to put it next to bananas. Apparentally the bananas emit chemicals or something that helps to ripen fruit 
Paprika wrote:Ive always been told to ripen any fruit to put it next to bananas. Apparentally the bananas emit chemicals or something that helps to ripen fruit
I think Im gonna try that one. We always have bananas in the house and I might try putting unripe mango next to it.
How do you know when they're ripe? Just give a little squeeze & feel for softness? I've never used fresh avocado, so I'm clueless!