This page and child pages will attempt to go over the major considerations when choosing items to use with hardware.
The general approach is as follows:
What specifications are given
Digikey filters or datasheets are a great place to start
Find out why those specifications exist, if applicable
FBSOA, Wire amperage, fuse voltage, etc.
How do those specifications affect your application?
Eg: Voltage drop, Power dissipation, frequency limitations, etc.
If there is a specification given that you do not know about, you MUST figure out WHY it exists in order to properly spec the component, or find additional cost savings.
For up to date component selection standards, see Electrical Standards. This Category is almost 4 years old but it provides a good understanding of components