I build fun scale antique and WWI types mostly which require lots of functional struts, wires and fittings to replicate. Wish I had more pics to show the 'shiny' soldered joints. If the joints are dull and 'globby' then the joint is not a good one. Heating and adding flux can cure it but a lot of times the parts need a good cleaning and filing to get the oils and/or surface oxidation off. These pics demonstrate wrapped wires, wire in tube and butt joint with fillets. I build jigs out of hard balsa to hold my parts and I get the jig wet to keep fire possibility to a minimum. Sometimes parts to be soldered are near previously soldered parts and you have a possibility of them 'un-soldering' much to your chagrin. If a jig can't hold everything or I am feeling a little lazy I wrap the part to be preserved and not un-soldered in wet toilet tissue to act as a heat sink. Remember, the flux is acid so it will 'eat' stuff it gets onto. Have a clear work surface and make sure any clothes you are wearing are from the 'Hobo' section of the wardrobe. There are other ways but I've been doing this for 40 years and it works for me! After you solder your parts wash them with spare tooth brush, soap and water then dry them immediately. I 'taste' the part with my tongue and if it is sour (flux is acid = sour) then I wash it some more until I only get a metal taste (clean). Yes- I have 'strong white teeth' (quoting a Benny Hill bit part!) and haven't dissolved them out of my head, yet! You are now the proud owner of soldered parts ready to be primed and painted! Good luck and practice makes.... an acceptable part!