Be fully carbed up, glycogen ties up water, you want your liver and muscles full of it. Drink as much water as you can stand in the 20-30 minutes leading up to the weigh in, and have full stomach, bowel and bladder on the scale. This is easy weight. Then you go into the final weigh-in with everything emptied out and carb depleted, that could be 15 pounds right there, maybe a lot more if you're hugely fat.
You can also gain weight (fat) in the days prior to, if you temporarily go a few pounds over your setpoint it should come off fairly quickly when you start to diet. The best way to do that is good old fashioned hogging, lots of sugared cereal, ice cream, pastries, etc. Morning noon and night, ad nausea.
If clothes are allowed for the weigh in, obviously wear as much as you can get by with, heavy corduroy pants, blazer, heaviest & clunkiest shoes you can find, etc.