More than just a vision, ubiquitous computing is applied in many fields of Computer Science and it has well been established. However, there are aspects which still need to be optimized and necessitate a more in-depth research to exploit even further the potential of ubiquitous computing. In this thesis we tackle problems and challenges of the ubiquitous computing in the domains of Wireless Sensor Networks (WSN), Internet of Things (IoT) and Smart Environments. Specifically, Part I contains an introduction to WSN, IoT and Smart Environments. Part II presents and evaluates two design approaches for WSN, a framework for creating personalized Smart Environments using WSN and an Airborne WSN for air pollution monitoring. Part III focuses on Crowdsourcing motivators and a Crowdsourced-enabled platform architecture. Part IV investigates Crowdsensing and Incentive Mechanisms while Part V proposes traversal strategies for Wireless Power Transfer in Mobile-Ad Hoc Networks. Part VI presents the conclusions of this thesis.