Check out TECH SHOP SAN JOSE some tops on how to create better welds using good prep and how to avoid destroying your material.
Step 1: Strip Platting
in order to start the weld you need a clean surface for the electricity to jump to. as well as having some problems with some coatings burning and inhaling the fumes. so it makes it better in both days. there are many ways to strip coating for metals I have another instruct able for that.
Step 2: Clean Off All Foreign Materials
remove all residues oils etc. all remaining metal shavings or paint dust or whatever. you can do that with just a rag or use a wet rag but make sure the material is dry. or you can use a rag with paint prep, paint prep or whatever. but make sure it does not leave any residue itself
Step 3: Welding: Tips
make sure that your shielding gas is on the correct settings for the distance you will be welding from also make sure you make sure that it is at the right heat and speed of movement for the type of welding. and to finish grind the welds and any splatter when you are done. also between welds depending on what you are using you might want to wire wheel the weld to get rid of the residue before you weld again over the top of it. also try to use a clamp on the material in order to allow you to use both hands during welding.