These tips are old news to those of you who weld regularly, but might be helpful to novices or those who weld infrequently.
-Weld only bare metal. Yes, arc welders (stick welders) are famed for welding through paint and corrosion, but you'll always get better, smoother and stronger welds if you grind or sand away paint and rust so you're welding shiny metal.
-Ground only to bare metal. A poor ground makes it hard to strike an arc and creates an inconsistent arc that creates an inconsistent bead. Especially with MIG welders. MIGS are exceptionally finicky about having their ground clamp clamped to bare metal, but that the ground point be as close as possible to the area being welded. Put the ground clamp of a MIG welder on the end of a planter frame when you're welding on the other end of that frame, and you'll tear your hair out trying to get a good weld. Move that ground clamp to bare-metal a couple feet from you're actually welding and you won't believe what a good welder you've suddenly become.
-The wire-feed cable on MIG welders works better if it's has no kinks or tight curves between the welder's cabinet and the nozzle assembly. Anything that inhibits wire feeding through that cable/hose can create an inconsistent arc and goofy welds.
-Don't even waste your time trying to weld with welding rods that have thick, puffy, flaking flux. They've absorbed moisture from humidity, and are junk. The best welds come from fresh, dry rods. Store rods in sealed containers to keep them away from humidity.
-And, as a general rule, 7018 welding rods are "universal." 7018 rods weld well in a variety of positions, create smooth welds, and is very user friendly. The familiar 6011 and 6013 rods found in most farm shops are equally user-friendly, welding with a "puddle" that cools and solidifies quickly, though they leave a slightly rougher weld than 7018 rods.