What do you do or say to teach your toddlers to play well with others?

I have a 3 year old daughter, but I'm really clueless when it comes to good playground etiquette. It seems to me like parents are either neglectful, letting their kids run around wild and not paying attention to them at all, or they're helicopter parents that hardly let their kids actually enjoy playing. My daughter is definitely going through a 'mine' phase, and sometimes freaks out over sharing playground equipment, or taking turns, or whatever. I try to talk to her about taking turns, but it seems like I'm spending more time reprimanding her than she spends playing now. If she tries to jump in front of waiting children I'll make her wait, if she pushes I yell at her, but I don't know what's acceptable or expected at her age when she's out, and what's the best way to deal with her sharing issues. Any advice welcome.