Identify who would need your service, learn and do sales. Make sure you believe you have a great service. If not identify your greatest skill and improve it. Books are generally great. Here is a great sales book: https://www.amazon.com/SPIN-Selling-Neil-Rackham/dp/00705111...
If doing sales sounds tough, it will start tough and then get easier. If people ignore you just keep going.
Build something for someone for free (assuming you are in a programming or similar field).
When selling the most important part is the immediate benefit you are providing - will you reduce your customer's cost, improve their sales, solve some problem they spend too much time?
RE: how do you find clients? What field are you in? Who would need your service? Identify 1000 potential buyers and contact them. Contact them by email, phone, use forums, go to conferences, talk to people one on one. Introduce your benefit to them.. Make sure you contact people who seem to have budget and good things going on. Build a website on wordpress that describes your service. Hang out in places where your audience might be.
There is a lot to talk about but most importantly you "do" something consistently, improve it and keep going if you get Nos. If you stop doing you will never get there, and if you keep doing you will definitely get somewhere good, then great.
https://www.amazon.com/SPIN-Selling-Neil-Rackham/dp/00705111...
There are many sales books that present scripts, in general I think they are useful to read for generating ideas, I would suggest never using a script that doesn't feel comfortable for you to say, I would suggest also thinking about fitting any script you use back into the larger theoretical framework from the above book
personally, I like the scripts presented in Stephen Schiffman's books, https://www.amazon.com/Stephan-Schiffman/e/B001H9PRO2/ref=sr...
mainly on the ground that none of them make me cringe to say (specifically the '250 sales questions' and the 'Cold Calling' books), what makes you cringe is likely to be a little different from what makes me cringe, so your mileage will probably vary
there are a lot of books in this general genre, check out https://www.amazon.com/Brian-Tracy/e/B001H6OMRI/ref=sr_ntt_s... and https://www.amazon.com/Zig-Ziglar/e/B000AP7VIY/ref=sr_ntt_sr...
I do think these books present lots of good material for brainstorming, but some percentage of both these books I couldn't say to someone without cringing (I would suggest listening to that voice in your head, if it'd make you cringe, it's likely to make whoever you're saying it to cringe as well)
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fwiw, these books tend to be exceptionally easy reads, so I suggest checking them out, taking what you find useful, and leaving what you don't