Great answer Liann!
To add to that, if you use the points for more or less recess minutes, you erase the points when you come back in for recess. Basically you are going to erase and restart any time you give a reward or consequence. Some other ideas are:
a couple minutes of PAT time (preferred activity time: this is where students get to do their own preferred activity, within your preset limits of course), choose your own seat in the class for this period of time, minutes to play mind soccer (gotta check it out! awesome review game!) or even more or less homework pages (keep in mind it's rigged. so say you were giving out 5 pages of homework. students have two extra smilies. you say "Oh I WAS going to give you 7 pages of homework but now I'm only going to give five" or if they have two frownies you say "well I was going to give three pages of homework tonight but there are two frownies, so three pages plus two extra is 5). Change up the rewards to make it more fun. But keep in mind the plus/minus three rule. You should never have the difference of more than plus or minus three. too much reward and they get lazy. To much punishment and they give up. As far as when you use the scoreboard? I would say anytime you get a lull in the classroom and you want to bring the engagement and enthusiasm up (so....often:)
Hope this helps:)

Andrea