The scales vary a lot depending on what you have eaten/drunk that day, your hydration status etc etc... They are good for TRENDS in BF% - but only if you use them at the same time under the same conditions. So if you are at the gym at the same time each day, after eating the same amount/drinking the same amount each time - they will be ok in tracking your progress...
In terms of other things you can do to get an accurate reading - nothing short of a DEXA or water displacement test every few days is going to be 'truly' accurate... it is a matter of monitoring your progress to make sure things are going in the 'right direction'...
The mirror is one of the best ways to track what your body is doing, but it will not give you a 'reading'. Tape measurements are a good way to monitor progress too - but once again, it will not give you an accurate BF%....
Calipers in the hands of a TRAINED person are pretty good - and they improve in accuracy the more sites you test (3 site vs 7 site) but they can also be completely inaccurate if you do not know how to use them and two different people can get completely different results.