I know this is an older thread but in the spirit of helping just a few things ive found.
Apart from the obvious heat settings equations etc and text book stuff heres some stuff you learn and go 'oh, thats better' in point form, not because its a lecture just easier to read
1) crooked lines: etch a line with thick cut off wheel. Etch not cut. Draw a chalk line, etch with grinder etc. On multiple pass fillets especially overhead this helps keep your line well and looks mint.
2) boring holes: its always handy with welds to tack both ends before welding it. It helps with hot short(cracking) when there is a spot of metal to finish on. With thin sections like general fab the peno is not xray so this wont hurt. Also if you tack it up with a good fit and run a grinder to slighty bevel about 1mm deep it gives the weld a nice finish. You wont need to grind it neat.
3) second guessing is something that all good tradies do, dont do your head in over it and sometime down the road confidence will tame it well.
But this is why over thinker get called to fix some stuff that others leave behind.
Over all its just like sex, its all about heat control, hand speed and willingness to get burned and you never stick your hand where you wouldnt put your.............
Anyways have fun.