Practice, Practice, Practice!!! I've had the longarm for just over 3 years now. In addition to more than 100 quilts, I've gone through 3 bolts (60" wide) of muslin for just practicing, and I still pull out the muslin to try new things. I have zippers on my leaders, so I have a practice sandwich on the zippers, and I can quickly try whatever it is that I want to do.
I've found that to get smooth curves I start at my point, visualize the end point and swing. DON'T try to follow a curved line, that's where you get the wobbles. Put on some dancing music, move your feet, get loose!
Have fun! This isn't supposed to be work, even if we're trying to make a living at it!