As above with vision and the cheater lenses, you cant always get your helmet clad head near enough to a joint on a space frame to see properly.
Plan ahead and position the welder so to keep the welders lead is kept as straight as possible while welding .
Blow out the liner with an air line frequently and keep the shrouds clean, a can of anti spatter is a must for both the shroud and work-piece.
Nothing worse than weld spatter come chassis painting time to chop up all your abrasives and fingers.
Get comfy, you dont stand a hope in hell of producing a good even weld unless you get your elbow propped against something. Worth a minutes thought.
Other than technique which I wont go into a successful weld is only the correct amps and wire feed Vs speed of weld. Too slow and you burn through, too fast and you are cold laying mig wire on top of the work piece with no penetration.
Below is a rusty un prepped piece of 3mm scrap welded with .6 wire . A butt weld, internal and external all done on the same amps. If the wire feed Vs amps is correct you can get away with very poorly prepped work and still produce a presentable strong weld. I have Lloyds two gas and arc certs ( long expired) but am self taught mig , these are just my observations from personal experience.