A good weld on bad metal is impossible, but a little more information - like the type and duty cycle of the machine you are using, the sizes of the electrodes and the heat or amps you're using for them, the length of your lead, the thickness of the wrought iron, the fit of your joints, the welding positions, types of welds, etc - would help with a better answer, but I can offer a few tips.
Make sure that your electrodes are kept dry at all times, and warm them - a hot box is good - before use. Make sure your polarity is right. 6010 is DC. 6011 can be used on AC and while it can be used on DC machines with reverse polarity it doesn't work as well as 6010. 7018 is AC or DC reverse.
Make sure you're using the right size or diameter electrode for the thickness of the iron, and the right heat. Start in the lower accepted ranges for the size rod and try shortening up your arc length, increasing your hand speed, and just barely staying ahead of the pool. Watch the angle on verticles, stay 15-30 degrees on down verticals and 10-15 degrees on up verticals; and try circular weaves rather than triangular weaves, and vice-a-versa.
Don't run past the cycle of your machine, let it cool. Make sure your lead isn't too long, the ground is good, and with DC you should be looking for arc blow - especially with wrought iron. It has the fewest elements added to it and it's molecules tend to be quite long, so while it's usually very easy to weld, it also is very easily magnetized by welding and arc blow often occurs.