When I learned to use strobes, I did it manually without a meter. I tested my strobes with each reflector or diffuser I owned using slide film to determine the guide number. I made diagrams and calculated the exposure and the ratio of the main light to fill. I had modeling lights so I could see the effect of the positioning of the light, and I could move the lights around during the shoot, but as long as I didn't change the distance between the main light and the subject, I didn't have to recalculate, and my exposures were always spot on.
It's easier with a light meter, but there's a lot to be learned by going through the process of testing for guide number with film, diagramming the lighting, and seeing how it works at the shoot.