In order to blend ice smoothly, the main thing to keep in mind is that you should add the ice gradually, and in smaller chunks.
If you throw in a large number of ice cubes all at once, your blender will likely have a hard time grinding them down smoothly. You risk clogging in the blender too if you add too many ice cubes at once. You should blend the ice until it is fully taken care of before you add more too.
Aside from this, there are a few other ways to make the experience as smooth as possible. You could try blending frozen fruits for example instead of ice. This way it will be easier for your blender to deal with the smaller pieces, and you also get a nice extra hit of fruit in your iced drink. Another option is to make your own fruit or vegetable ice cubes. These will add extra flavour and can still cool down your drinks or desserts.