This is a very good question and lots of people will have a different take on what makes a good logo. That doesn't mean one is right and one is wrong. People just look at it from a different angle.
For me there are five key things a logo has to be - memorable, simple, appropriate, easily recognisable and finally (and really importantly) your logo has to work over a variety of media types.
MEMORABLE - people like familiarity, it makes them feel comfortable so a logo that is memorable is a must. You want your customers to remember you and remember the experience they had with you so when they see your logo again they want to come back.
SIMPLE - An over complicated logo doesn’t tell potential customers what you do. Keep your logo simple so it’s message is really clear. If your logo is complex then your customers won't understand what you do.
APPROPRIATE - when thinking about a logo then make sure it is appropriate to your business. Remember the logo has to represent you and your business.
EASILY RECOGNISABLE -.you want your customers to recognise you when they see your logo. Think of some major brands and their logo. You recognise that logo the moment you see it.
Finally, and probably the most important for me is YOUR LOGO HAS TO WORK OVER A VARIETY OF MEDIAS. When designing a logo something I always want to know is where is the logo going to be used? Social media platforms can crop your logo so it needs to work in these situations.
Have a look at how small your logo appears at the top of your Instagram page. You need your logo to be memorable, simple, appropriate and easily recognisable even in this tiny round circle.
When I am designing a logo I follow these rules to make sure my designs work for my clients.