Take good photos, on a nice day outside.
Describe the product well if you know the details of the product.
Fix or repair anything is broken that is a low hanging fruit, i.e. if your bike has a puncture replace the tube for 10 dollars by buying a tube at a store and doing it yourself. A bike that can be cycled instead of walked is much more sellable.
Be honest about the description, if you are aware of a major flaw make someone aware in the advertisement. Don't lie about something being fine when it's not.
It sucks to be on the wrong side of that.
Post the ad for free online if possible, facebook marketplace, kijiji, craigslist or other local classified sites with some volume of people on them. If you pay for an advertisement make sure it is worth it, and make sure to include the cost in the sale price of the item to recoup the advertising costs.
Finally on pricing, price the item more than you expect to get, be patient. If someone offers your real price or above, accept the offer, or if some people want to view the item and test it let them. If you have a price in mind, don't go below the price.
For example I bought a bike for 200$ spent $10 on repairs and no longer use it.
Post an ad online for $300 dollars, get a few people to view it and a few offers in the range of 170-200$ or 230$ subject to viewing.
Drop the price each week by $10, so people who follow the ad know the price is dropping.
So on week 3 someone came to view it for the price of $270 (on the ad) but no offer made in advance of viewing, I let them test the bike and when they were happy, they offered $250 and I accepted. They thought they were getting a deal as they negotiated the ad price down, it's in their head they saved 20 bucks. I knew I was getting a deal as long as I covered $210 + the cost of my time doing minor repairs.
I made minor profit on this but will be giving the money to a bike store to fix my other bike, so it's going back into the cycling ecosystem to pay the bike mechanic and parts. I'm not operating a cut-throat get rich quick scheme.