How do you ZigZag?

I've heard a lot about zigzagging calories. It has always frightened me. In my head it does not seem logical to go over you calories to lose weight. However... Last month I did a full round of 30DS paired with staying under my calories. I did well, lost a total of 9lbs. Then went on vacation and for 2 whole weeks I didnt watch what i ate. Lost 1lb while eating crap food. Then got home started watching what i was eating again and lost 3lbs just like that. Since the 3lbs my weight loss has slowed big time. I want to zigzag again but Im afraid too. I guess my biggest questions about it is How do you zigzag your diet? How many days on and how many off? I was thinking for myself maybe do 3 days off then the remainder of that week plus one full week then 3 more days off and so on? Any tips would be great, thanks!

-Kristyn