Rotate your arms. Try it on flat ground. Windup and then whip your arms in the other direction. Keep your arms completely level. As your arms get in front of you turn your head with them to the other side. Look over your should until you see the landing and complete the spin. 180 to 360 is one of the biggest obstacles. For a 180 you can jump up in the air and 180. For a 360 you actually have to learn how to spin.
I'd recommend learning on something small that you're comfortable with. I would say something mellow and not to poppy to help you stay level. If you feel like it's not working go back to flat ground again. It's all in the windup and release. If you throw your arms level, and hold your head over your shoulder you'll keep spinning. 3-5 is another milestone but not as hard imo. For that you have to get used to NOT focusing on the landing when you come around 360. Where your head goes your body will go. If you lock your eyes on the landing at 270 your going to stop spinning at 360. If you want to 5, trust yourself and hold your head until you're about 450.
Keep practicing. One you figure it out it'll be NBD. Good luck