There are the usual pertinent questions that can be googled, but upon selecting a contractor please ensure that one fully understands the contract. Based on professional suggestions, might want to consider seeking legal counsel to at least review contract and advise changes in vague language, as the contract is provided by the contractor and is written for their benefit and protection. When problems occur, both parties will refer to the contract language (clarity or vague, & open to interpretation??). Also need to have a very detailed material spec sheet, think about every detail of construction and make sure it is in there; ex. texture on wall & ceilings (smooth, light orange peel, heavy......). If using any tile, break a piece that will be used and have all parties sign pieces for reference. I could go on, but documentation is critical and protects all parties.