First you want to figure out what type of switch you want, there are several different combinations of weight, tactile/linear and clicky/non clicky (these are referred to by colour, eg Red, Blue, Brown etc). There is a good overview here.

This is the most important factor by far, and you shouldn’t buy a keyboard until you understand how each of these switches feel (and sound, if that’s a potential issue).

I like blues, myself, because I find them the most comfortable for typing. But they’re not necessarily ideal for gaming or cohabiting.

Try to go to a store which has a bunch set up next to each other, and go from there.