"It's good to learn from your mistakes. It's better to learn from other people's mistakes." - Warren Buffett
There's a whole lot to know. Too much to try to tell you in a brief post, but my advice to new investors about when they are ready to invest is simple. When you know a good deal when you see one, you are ready to start. How do you know a good deal when you see one? By knowing your market (whatever market you invest in if not local).
There's a ton of money spent marketing real estate and you can learn a lot from it. The more you look at what's for sale and pay attention to the size, features and amenities of the properties and you will start to get an understanding of what's a "normal price" for a property in a given area. When you start to notice "that's a high (or low) price" for a property in that area, that's when you start to know your market.
I did this with newspapers, but there's a slick way to do this with today's technology using the realtor.com app. If you use the app, you can just click on "For Sale" on the main screen and all "Active" listings around you will show up in the palm of your hand! Use the "scout" option at the bottom of the screen and it will show you listings and their prices as you drive around! It is only active listings, so if there's a sale pending it won't show up and there's no sold data there either. Still very useful information IMO.
One other point about knowing your market and I'll stop before this becomes a book. Look for value boundaries. Look at where prices change from one area to another. Before long you will get an understanding of why the automated valuation models (like Zestimate) are often so inaccurate. A house 5-6 streets away might be a better comparable than one on the other side of the street if that particular street is a value boundary. These types of things are psychological and matters of local knowledge and that's kind of hard to program into an algorithym.
In the long run, real estate investing is very forgiving of mistakes you make as you learn. I think rule number one is, "make your money when you buy."