First thing would be to pick a platform and start experimenting
For IOT you will need internet connectivity so
Raspberry PI starter kit
Arduino Yun + an arduino starter kit
TI Launchpad CC3200 or TI Connected Launchpad
any of these will work to get you started, the PI is linux based of course so may be a plus for you depending on what programming exp you have
all can be programmed with C and can connected to the internet, there have been many road tests and challenges over the last few months all involving internet connectivity, have a read, pick your platform and play away for a while to learn, there is no "Best" one, it all depends on your likes and dislikes and there is plenty of support no matter which you choose
About the lowest cost platform is the PSoC4 Prototyping Kit (CY8CKIT-049 42xx) from Cypress Semiconductor (about $4) and the development software is completely free and unrestricted. (PSOC Creator). This module is significantly more powerful than a low cost arduino, however this and most other low cost platforms doesn't include a full internet connection, it only has a USB interface which would need to connect to another computer that is on the internet if you want a complete IoT system.
To get started Element14 ran a great series called 100 projects in 100 days - all on PSoC4 applications. They used the Pioneer Kit, but can all be adapted to the Prototyping Kit which uses the same MCU.
