Martin Lewis from MoneySavingExpert.com has written a guide for people wanting to check whether they are in the correct council tax band.
By far the most important step is to find out if your band's higher than neighbours in similar or identical properties. You could simply ask them, but there's no need as it's public info. The band of every house in England is available here.
So first check your band, and then your neighbours'. Make sure the properties are as close as possible in size and value. Sadly, the sheer scale of the database means a few properties are missed off it. If that happens, either speak to your neighbours directly or contact the council and ask why. If neighbours in similar properties are in a lower band than you, then you may have a claim.
A second useful step is to estimate what your house was worth in 1991, as that's when the council tax bands were defined.
This CAN'T be used as evidence in appeals. But it enables you to check out various house prices and it's an important test that you're on the right track if you decide to appeal.
First - value your house. If you bought your house after 1991, you can simply use its price and date of sale to do this. If you rent or bought earlier you'll need to find an estimated price.
Now - find what it was worth in 1991. Once you have that information, you can use it to estimate what your property would've been worth back in 1991, and what band it's in. MoneySavingExpert.com has built a calculator to do it for you, using house price data from Nationwide.
Challenging your band is not something to do speculatively without the checks, for one simple reason:
You can't ask for your band to be lowered, only for a 'reassessment', which means your band could be moved up as well as down.
It's even possible that your neighbours' band could be increased, although this is extremely rare.
If you're convinced your property band's unfair, it's time to challenge it.