in your protest message (about 1000 words), you need to use CMA (similar houses sold last year around you) to come up a value for your home. County appraisal office will respond within two days either with hearing date or a deal. If it is a deal, then you decide to accept or decline, you will have a hearing date if you reject the offer. You can request House Bill evidence packet from them to see how they arrived the appraised value by written.
You need to take lots lots of photos inside and outside as evidence, and get on google earth to see anything else might impact the value, such as, busy road, real road nearby, water tower....
i live in Collin County near Dallas, a group of us use a tax firm to represent us; we are also protesting in city council meeting to rollback property tax rate.
Hope this helps.