Common things that seem to show up on most any board you make.

First comment: Read the datasheets for all of your components to save headaches later.

• UMicrocontroller (at least one, probably…does the processing)
• Programming port — you need a way to program your MCU. This takes four signals (VCC, GND, TST (test), RST (reset)). RST needs a pull-up resistor (normally 47k Ohm for MSP430s), and 2.2nF between RST and GND.
• Debugging ports — Plan ways to get information back from your MCU. UART or SPI. UART is natively supported by Energia (if you’re using it). You can also use Minicom or any other serial reader to get information from the UART. FTDI chips translate UART signals to USB for your laptop’s consumption.
• GPIO pins — it’s useful to have a few test pins that you can drive high and low to measure stuff.
• Jumpers — if you can, design independent circuit components so that they can be physically disconnected from the rest of the circuit. During testing, when things are not going well, this is super handy. Use the little 1.27mm jumpers.
• RTC or Crystal — typically attaches to two pins on the MCU. Think about timing needs before-hand.

• Bypass capacitors — placed between VCC and GND to smooth out power line spikes. When in doubt, use them. Typical sizes
• Voltage regulators — Buck (step-down) converters convert a higher voltage to a lower. Boost (step-up) converters convert from lower to higher. Switching regulators are often more efficient than linear regulators, but might be noisier. Don’t step down too much voltage when using a linear regulator because they get hot. With switching regulators pay careful attention to board layouts (copy them from the datasheet).

Planes are regions of your board that are all connected to a signal (usually power or ground). Planes help reduce noise. In Eagle, use the Polygon tool to make them.