This article can give you a start on learning how to properly cut weight.
Make sure you read the warnings.
http://fourhourworkweek.com/2013/05/06/how-to-cut-weight-ufc/
When I started learning how to diet down and cut I looked to GSP as an example and starting point. Mostly because he spent a lot of time and money surrounding himself with people to help keep him on top. I follow a very similar weight cut as GSP. I played with the concepts to hone them specifically for me. Some of the differences in my plan is I eat a lot of fruit. After an 8-10 week training cycle my metabolism is so high I'm not worried about the sugar carbs. Plus the natural sugars help my mental state during cutting and keep my energy levels up. Another difference is I'v never had to use a sauna, sauna suit or extreme exercise during cut week to lose the weight. This is mostly do in part beacuse I increase my metabolism during an 8-10 week training cycle. The final touch for me is I do a 36 hour water cut and 24 hour food cut before a fight.
For rehydration and weight gain I pretty much follow the same process as in the article.
Reminder: read the warnings