Macau is small so taking taxi is also reasonable sometimes. On the other hand, most of the large hotels and casinos do supply free buses, which will be helpful and save transportation fee for you. For example, if you come to Macau from HK by ferry, at the ferry terminal you could take the free bus to Hotel Lisboa firstly. From this hotel,you could walk to visit the Sanado Square and the Ruins of St. Paul's. Or, you could take the free bus to visit the Venetian Resort.