THE ONLY THING A SIDE-HUSTLE NEEDS? CUSTOMERS!

No customer. No money. But of course you probably knew that part.

The part you might not get is exactly how to go about gaining customers.
More often than not it's the hard part.

Ideally you want them (your customers) to come to you.
Thats not impossible, It's not even unrealistic. In fact many a side hustle got started with a neighbor's request for help resulting in a light bulb going off.
The reality is that you SHOULD have customers, or at least any number of potential clients prior to embarking on any serious side hustle endeavor.

Lets look at the example of a side hustler.
Bill has a regular job and is doing a little better than getting by. 
Not a lot better but still.
He decides that in addition to his healthy 401K contributions he makes at work but he wants more. 
After much consideration he decides to limit his side hustle job to the summer only.
With a handful of customers already, Bill decides to make an extra $7000 a year during the summer cutting lawns.
This additional money, after taxes and up-front cost will be put into a Roth IRA every January.
Depending on Bill's age, ability, and investment decisions this could over time represent perhaps a million or more tax-free dollars or more for Bill and later his heirs.

So what have we learned from Bill's decision.
Bill had a few customers to start with, knew exactly what this money would be used for and how much.
He also chose a side hustle he knew he could really do.

Most likely Bill's summer only side gig has dramatically changed his future.
It very well may have changed his family's future as well by creating generational wealth.

Side hustles are cool like that.
They can quickly change both your present and more so your future.
None of this matters though if you can't get customers.
The number one driver of customers is your reputation.
 Do good work on every job you take and exceed your client's expectations.
Even better than gaining a customer is gaining a repeat customer.
Your reputation should eventually become your most profitable channel. 
No ads necessary.

Until then, your going to have to go about the more traditional methods to get customers.
This means former clients, neighbors, or other people you see you think could use your services.
Craigslist, Facebook Marketplace, online bulletin boards, real neighborhood bulletin boards, co-workers (just make sure theres no work conflict ) Friends, church, and other places.
 Getting side hustle customers is part of the work involving side hustles.
In fact it's often the biggest part.

Some things that you need to remember.
Not all customers are good customers. 
A bad customer is the only thing worse than no customer at all.
Don't try to undercut everyone and don't make unrealistic promises.
Treat the customers as if they are always right unless they prove otherwise.
Communicate clearly with the customer on all important matters,
Also. Everything done should always be put in writing. It lends credibility to your hustle as a professional, not to mention this serves to lower the chance of being ripped-off.
Not all customers are worth having, 
Don't low-ball, and don't try to be everything to everybody.

BCS recommendation:
We don't do a lot of recommendations and aren't paid to make any but theres is one book I can recommend.
I came across it in the local library where you'll probably find it as well.
Its a book called “Guerrilla Marketing Remix: The Best of Guerrilla Marketing,” published in 2011.
Its a little dated and doesn't take into account online marketing themes like newer books of the same sort would  for but it's still a great book thats (hopefully) bound to get you all the customers you could handle.

The best part is that it currently sells for about $7 plus S&H.