If there is a specific type of prop you want to build, or a specific style or medium you want to work in, find the companies that specialize in that. Fill your portfolio with that kind of work. If you want to build sci-fi weapons for instance, but all your previous work is in constructing furniture, employers won’t necessarily make the leap that your furniture construction skills will translate into sci-fi weapon-making. Even if you have to build your own props on your own time, do it.
This is also true for skills you lack; a lot of theatres with a one-person prop shop are looking for well-rounded prop makers, which includes being able to upholster. I never learned how to upholster, so I started practicing it every chance I could get, and taking on any little upholstery project I could.
Once you are out of school, no one will be around to guide you with what you need to learn next, so you should always be experimenting with new skills, new materials and new techniques.