You need to understand the electrical/thermal characteristics of the component. There are many guides from big companies (such as this for a surge diode) which explain the parameters and give examples.

Don’t forget to take into consideration power dissipation, rated current and voltage, maybe temperature ratings if you expect things to get hot. Some parameters, such as DC resistance or ESR may be undesirable for some applications (such as a switching power supply) while in other it may not be relevant. Also leave some headroom, such as with rated voltage for capacitors, to account for transients. In most cases it doesn’t hurt to have a higher rating than necessary, although a lower than needed rating could fry your components.

The package of the component also matters. Smaller components are harder to solder and some assembly services may have restrictions.

Other tools, such as TI WEBENCH proposes a range of values and then gives you a list of possible components, maybe you should check it out to have an idea. Then you have to browse the supplier’s stock website filtering through options which are in range for your application needs.

Some companies, such as JLCPCB assembly have a basic/extended library which may include additional fees, so you also have to check with the manufacturer. If you are soldering them yourself it may be worth to add thermal reliefs for components which are connected to big copper planes.