I live in a state where they fully expect you to challenge tax assessments on your property and I'm shocked at how easy they make the process. There are even reputable companies to challenge the assessments for you (reassess a fair price and go in person to represent you for a small fee - only paid if they get a reduction on your assessment).
That being said, it was very easy for my house. I've done it the last 3 years. The county tax assessor's office provides paperwork in the package to protest. You can do it online or by mail. You'll need to check in with your local office to find out if they don't make it really easy to figure out (did you check through all the paperwork they sent you to see if they have a protest procedure?)
I protest based off the idea that my house needs major repairs and is very basic builder grade everything, and would not sell for anything near the average market price. I take LOTS of photos, set up a word doc containing them and descriptions of the problems and in the case of several comparisons also pointed out where I have builder grade items installed, while the houses they are using as a basis for comparison have upgraded items (like cabinets/countertops, flooring, etc).
This is the one time where you want to sell someone on just how awful and messed up your house is. So I don't hold back - anything that needs repairing or is deteriorating is fair game. Special emphasis on roof, electrical, plumbing and other structural issues. Cosmetic stuff like paint or carpet are not usually weighted very heavily, but when I show up with PAGES of stuff, they take into account that replacing carpet or painting a whole house might also cost some money and need to be included in an overall assessment for value.
I've never failed to get a significant reduction using clearly labeled photos (and I do make copies - one for me and one for them to keep). So for about an hour of taking photos and then labeling them in a doc, then printing out a few copies and then attending the actual meeting (maybe an hour waiting around, and 15 minutes to go over everything?) I have gotten at least a 15% or better reduction. I think it's worth it.
But if your house is relatively new and has no real issues, you would have to rely on the comps for what homes are selling for in your area. You should be able to pull that up through websites like Realtor.com or like someone else mentioned, check with a real estate agent, but you might be screwed for any significant reduction if your area is hot and houses are selling at a premium.