To do liberty work with your horse you have be very aware of your body language. If you watch horses out in the pasture 99% of how they communicate is through body language. It starts in the round pen.
When I ask them to go I point up high in the direction I want them to go in, kiss, and if they don't go I will then use the whip. Always starting with the least amount of pressure, but will do what i have to get the job done. (suggest, ask, tell) Eventually they will get going off of the suggestion more often then not. When the horse is going around you want your body behind the drive line to encourage forward movement. (the drive line is where your imaginary girth would be) Try to keep your belly button pointed behind it. Whenever I work with my horse I want her to use the thinking side of her brain instead of the reactive side nature gave her. How do I get her to do that? By making her move her feet, and doing a lot of transitions and changes of direction. In the round pen to change direction you step in front of the drive line and run (RUN!) backwards when you have two eyes point and move back toward your horse to encourage her to move again. If she turns into the fence cut her off and make her hustle for a lap or two. When you get her turning in consistently, have her come in and rest with you. I usually use this time to desensitize her to one of my tools. (lead rope, stick and string, stock whip, plastic bag etc.) After she has had a rest I will get her to follow me by getting her hindquarters moving and walking in circles. (prey animals like walking in curves instead of straight lines) If she get confused and leaves just make her hustle again then come back and rest with you. It doesn't take them too long to figure out they want to stay with you and rest.
When you feel like your horse is really good in the round pen then you can try a small arena.
I got really good control of those hindquarters with the halter and lead. If i look at her hinny (Act like you are going to step on her tail and bow.) it better move away and she should give me two eyes. (In my video you can she me getting her to yield her hindquarters a lot when she is going over the poles and at the tarp.)
I'm sure I'm forgetting stuff, but that should help get you started. Hope that helps. Liberty is really rewarding and a good challenge for your communication with your horse.