Turn up the power to warm up the rod, then turn down in small stages until the arc is not too violent.

Always use a mask, with the correct filter

Make sure you have a good clean earth connection and that the rod end has a clean connection to the holder.

Always use a mask.

Clean the metal with a grinder before welding, just run a weld onto a flat piece first, dont try and join two pieces. Practice on a thick piece not thin sheet. Dont drag the rod too quickly.

When you eventually start to get good welds the slag on top of the weld should fall off very easily in large pieces.

Did I mention using a mask with no cracks in the glass.