I started liberty with my mare by positively reinforcing each time she showed any interest in me. Even the smallest amount of interest, like her ears being on me or even taking a single step toward me when I called.
The logic behind it at the time I didn't understand, as I was just maybe 8 or 9, but basically if your horse shows ANY interest in you at all, release ALL pressure and reward. The best kind of positive reinforcement, I have found, is treats. If I were you, I would make sure your horse has very good food manners to not become pushy while you are working on teaching liberty.
So, to start off, make sure your horse has good food manners. Next, ensure your horse has good groundwork skills ON the lead rope. The dictionary definition of liberty is "the power or scope to act as one pleases." So, even your horse just allowing you to tack them up without being tied anywhere or forced to stand still is liberty, just not what you are wanting. As long as you give your horse a choice, it is liberty. Your horse WANTING to be with you without being forced, now that is the hard part. And it is not because you're terrible and your horse doesn't like you, but it is just in their nature to want food and be in an environment in which they can survive, and following you around doesn't always offer that.
So, how can you reinforce your horse being around you? Well, that brings us right back to positive reinforcement. For a quick rundown so you can skip whatever I am about to ramble on about, positively reinforce yourself like you are teaching your horse how to do a basic command like back up. Be repetitive and communicate what you want in a positive way. Use less negative reinforcement (taking off a bad/annoying thing, like pressure) and use more positive reinforcement (adding on a positive thing, like treats). It is so hard to have a horse that wants to be with you because it is intrinsically rewarding for them, however it isn't impossible. Besides, you have to start somewhere. If you can get your horse extrinsically motivated to be with you, then find out what they enjoy doing and start doing it with them. Show them being around you is better than being alone, so then they will want to be with you just to be with you, not for a reward.
This is my first post on here, so I am not sure if it will make sense as I am new at writing stuff like this lol. But I hope you, or whoever may be reading this, can find some value in my nonsense. And, if you have any questions or want to talk one on one feel free to message me. I'm up to talk to anyone and try to help anyone, don't hesitate to shoot me a message!