To improve WiFi signal strength across a large office, consider installing additional access points, using WiFi extenders or mesh networks, and strategically placing routers and access points for optimal coverage. Also, ensure that your network is on the correct frequency band (2.4 GHz for longer range but slower speeds, 5 GHz for faster speeds but shorter range) and that devices are not causing interference. Regular network audits and updates can also help in maintaining optimal performance.