A few thing then might help
One is drawing from the inside of your arc. IT'll take some practice to get a smooth bump free line but try for long lines in about the right direction. You'll need a loose grip on your pen. If you draw from the inside of the arc though, you'll more likely get a smooth line cause that's the natural path the wrist makes
My next thing is rulers. No necessarily the straight kind, but you can get French curves, and bendable rulers. These will help a great deal with longer curves. Again though, a loose hand is key. Relax, and keep your lines flowing and not stiff
Some say to hold further up your pen / pencil to get relaxed flowing lines. As long as you're not holding the nib though you should be fine.
Oh- and turning the page is totally ok
Don't make your arm uncomfortable moving it. Just turn the image around till it's comfortable to draw a nice arc. Hope it helps