When I first started also at 17 websites hadn't really been utilized, i.e. weren't popular enough for people to go looking for you. I didn't even have an email address or a cell phone, it was pager with voicemail all the way. I think I sound like a grumpy old man saying, "in my day…"
Anyways, in '97 I started with my older brother and detailed for about 3 months. At the end of that summer I realized that I could do pretty much everything that my brother was doing and make his share. He went back to college and I took over one of his fleet accounts, 6 trucks at $10 each once a week outside only. We mostly cold called in a wealthier-than-our-own suburb of LA and when he left I stayed in our own town and built my own route.
In about 6 weeks I built a route that was giving me take home pay of $2k/month working ~20 hours a week. Each week I chose certain areas of town to work, I'd visit the business parks and walk into the businesses and say, "Hi my name is Hank and I'm in the area washing cars would you like your car washed?" some said "no", some said "yes". I'd go to the same place each week at roughly the same time and since they knew me I'd just ask if they wanted a car wash, people are busy. Over time more and more people said "yes". I always tried to make it sound easy for me even if I was desperate for work, in a way I was creating an air that wether they used my services or not I didn't care. Which in the end I think made me seem more valuable, I guess i was playing hard to get in a way.
Most people want someone to have confidence in, so I think if you do a good job consistently, show up consistently(even if it's a slow spot for a few weeks), and act confident, then people will trust you. When it comes to building and maintaining loyal customer base, trust is key.
A couple other random things I've learned:
It seems to me when cold calling most people just want a wash, when you wash the car you keep your eye out for things. Nine times out of ten they'll need a wax. Often I'd test an area, like a small spot on the hood and when I went to collect, I informed them of the issue and told them I'd tested a small area. Usually they'd follow me out and we'd look at the area together, adding the wax was a slam dunk. Everyone was happy. You have to be careful though, some people might get pissed at your initiative, fwiw I'v never upset people with that approach.
I also found that I made most my money before noon, the afternoon seems like a much better time to schedule future visits, waxes, details, phoning businesses and asking who handles the fleets, etc.
Always lace, ask your customers, "Who do you know that would like my services." Asking people about people they know will generate leads. I've had people personally call for me cause they were so excited. Remember to ask "who they know" rather than "if they know", the answer to "if" is usually "no".
I'd take on a couple fleets too, they can be quick easy money. Charge more than $10 though
Hope this helps, and good luck.