Ideas for supporting positive behaviour in pre-school/playgroup settings:
Stickers - always very popular!
Positive language - rather than "Don't run", try and say "Can you use walking feet?" etc - and it is also important to praise positive behaviour to encourage others who are misbehaving - e.g. "Well done, Ben, you are walking so sensibly/sitting so quietly" - which will generally ensure that the rest of the children walk/ sit still!
Pictorial references to rules around setting to reinforce 'nice/appropriate' behaviour - get the children involved in these displays, possibly getting them to role-play situations for photos?
Children often misbehave for attention so taking away attention can work - i.e. ignore them when they misbehave, turning your back on them and comforting any child who has been hurt instead.
To deal with recurring bad behaviour, you may need to use the ABC method - Antecedent (what happened before the incident) Behaviour (what actually happened) and Consequence (what happened next) Logging these could show up why negative behaviours are occurring, making it easier to deal with. May deal using reward/stickers charts, home-setting books etc
Hope that helps