I'll be honest, learning how to use the sling was not easy for me. In fact, I ended up cussing it out as I took my daughter out of the knotted mess while she screamed her head off. LOL. BUT, it has gotten a lot easier. I also found that the cradle hold was not the best for us. I have large breasts, and to wear her high enough to wear I felt comfortable meant that her head was smooshed into my boobs, making her neck look crooked.
The only thing I can say is to hang in there and keep practicing. Always make sure baby is in a good mood (well rested and fed) before trying it, and experiment with different holds.
My daughter really likes the front hold, where she is upright against my chest with her legs out the bottom wrapped around my waist. You might want to try that one. You can also pull the fabric up so that her head is supported as well.
Also keep in mind that when they were in the womb they were squished into a little ball, so quite often they enjoy being squished into a little ball in the sling too. It's ok if their head is to one side, or if a leg is pulled up (even though we might not like it). Believe it or not, your baby will tell you when it's time to change positions, usually by trying to stretch their legs out.
As for tips on doing it up and adjusting it... make sure the fabric is evenly spread out on the rings, and that the "rails" are not twisted, otherwise it's impossible to adjust with baby in the sling. Practice with a bag of flour in there (seriously, it worked for me!). And do it front of a mirror, that really helps too.
I also just recently orderd a wrap because I liked the idea of it going over both shoulders. I'll be sure to let you know how I like it. That one has no rings, but you do have to tie it on, so I'm not sure it will be any easier.