I have had success sending a personalized email (or LinkedIn message) to a targeted company. In my case, reaching out to precasters and manufactures in my industry with a cold email and explaining how my services can benefit them has had good success. However, I am in a very small niche (mainly MSE, SRW, and rockery retaining walls), and I am usually fulfilling a pain point for that precaster/manufacturer in them selling more product if their clients can get engineering performed. So, them being able to send a quote to a customer with my contact information for engineering helps them sell more product without costing them anything.
I have also had success taking on projects from contractors that seems slightly sketching at first, but were doing high end residential work. Turns out they were not sketchy, and they introduced me to their architect doing high end residential, and now they send me all their retaining wall work.
Attending contractor trainings has also been a huge success. In addition to being informative on what questions contractors are asking, I had about a dozen people come up and tell me their pain points with engineers and ask if I could help them and get my business card. It helped that I was the only engineer there in attendance, and I made the presenter aware of that.
Now, I do very little cold emailing because I have plenty of work. I get a lot of new clients through my website now. When I first started out, I did a lot of blogging, and it didn't pay dividends up front, but now that SEO has really kicked in even though I don't consistently post blog posts now.
I think the biggest question you first have to answer is what pain point are you solving for your customers or what can you provide that other firms cannot (be careful not to compare yourself to other engineering firms in any marketing as this violates engineering ethics). If you have that solution, then include that solution in your cold email, LinkedIn message, website tagline, etc., you should get higher success aquiring customers.