Traces that carry large currents should be wider to avoid heat buildup. Use this calculator to decide nominal trace widths
A thermal relief pad is a printed circuit board (PCB) pad connected to a copper pour using a thermal connection. It looks like a normal pad with copper "spokes" connecting it to the surrounding copper. Thermal reliefs are used to make it easier to solder components to the board due to the hight thermal conductivity of copper. Read more on thermal reliefs on wikipedia
- round leads: add 6 mils to the nominal round lead diameter to get the recommended PCB hole diameter.
- Rectangular leads: find the lead diagonal sqrt (x^2+y^2). Then add 6 mils to get the recommended PCB hole diameter.
Traces caring high voltages should have adiquiate spacing. Spacing is a function of voltage. Use this guide for calculating safe distances.