How do you get companies as customers for image shoots and bill them correctly?

Hello,

I now work part-time as a photographer and videographer, and I also handle the design and acquisition of print and advertising media. What's the best way to get companies as clients? I would like to print flyers and business cards. Should I just contact the companies via email? Perhaps with a few pictures and videos.
I'm also still unsure what I can charge for my work. Do you have a guideline?

Thanks