Cheat!! Look at what other people have used.
There are always projects in Electronics mags & on websites.Some articles actually spend time explaining why they chose particular components.
If you can,look at real,commercially made Electronic equipment.
After a while,you will get a "feel" for the standard component types used in particular sorts of circuits.
Your design may not be like any of them,but you will recognise similar situations,& be guided by them.
It seems many people feel this is "copying" & would rather rely on their own ,sometimes immature design skills,with the result being a good idea,but spoilt by poor choice of components.
VK6ZGO