My name is Luke, I am a Product Growth Manager and specialize in building, marketing and growing tech!
For your question here there are a few things you will want to do first:
1. Establish A Budget
--This is extremely important to do because it will dictate the direction in which you build your company and ensure that your resources are going to the most important things first.
2. Identify Goals
--Jot down your short term goals and how you hope they translate long term. This again will help shape your marketing strategy so it is focused on an end result.
3. Identify Your Audience
--Create a "avatar" of who you feel your typical visitor would be. This is important to do so you can ensure that your design, ux, marketing, messaging etc. speaks directly to them.
Now here are a few suggestions on how you can better build and monetize a classified business.
1. Focus on a niche
It will be very tough to succeed if you go too broad because there are just too many big players to complete with. Plus, on top of that you have things like Facebook Marketplace and independent Facebook groups that are killing it right now. By setting up a classified site to focus on a niche (ex. electronics) you will have a better chance at establishing authority within your market.
2. Embrace the "support local" movement
Focus your branding on your specific town / area. By doing so you are going where the big guys can't. You are a member of the community and make sure they know it. This should give you an edge and allow you to better build a local audience.
3. Build an audience
Getting someone to post a classified on your site really won't be the hard part... the hard part is getting an audience that is interested in what your site is offering.
Establish a social presence on Facebook and Instagram. Build out mailing lists from your site (ex. listing update alerts). Hold contests, take part in local events, blog etc. etc.
Once you build that audience / community around your brand, you will be able to more easily monetize it through things like paid classified posts, boosting / marketing classifieds, advertised posts / emails etc.
This is just a real macro overview of things but if you would like to talk more feel free to schedule a followup call with me!