1. Keep the soldering iron point clean, using a wet sponge or cloth will help to remove the oxidated layer and make sure you can still melt the tabbing wire.
2. Hold the soldering iron like a pen and keep it perpendicular to the table surface when trying to melt the wire.
3. Be patient; when you see the tabbing wire go molten into a semi liquid state that is when you should move the soldering iron. Doing so beforehand will be ineffective and take more time.