Good advice from beefy. Takes a while to get the “touch”.
Never tried croc clips though fifteens, I just used wet toilet tissue packed around the bulk parts. As long as it doesn’t stop hissing, you can’t damage the metal. To be honest, it would be difficult to melt a whole figure, but making holes is quite easy…..
I would say 70DegC solder and the correct liquid flux are essential, as is a fine tip (about 1mm) on the soldering iron. You can do it with 145DegC detailing solder, but that is sailing pretty close to the wind. I use Carrs 70DegC solder, a 40%phosphoric acid liquid flux, and an Antex 15 watt iron.
Hold the parts together mechanically. Blue tack works well. Like fine painting you really only want one thing moving to minimise the chance of errors. Next liberally flux the joint. If you can get a bead of flux to stand on there all the better. Next, put a very small bead of solder on the iron. 70 solder is funny stuff. I find it best to make a “smear” of solder with the iron, then cut out a suitably sized scrap and drop it on the iron tip with tweezers. Next just touch the solder on the iron tip to the surface of the flux on the joint. This will heat the flux but not the metal. There will be hissing as the flux boils away, but that’s OK. Flux boils below the melting point of the metal, but above the melting point of the solder. Remove the iron before the hissing stops and you shouldn’t damage the model. The solder will remain liquid in the boiling flux and will be pulled into the joint, glueing the parts together. Once the joint cools you can remove the blue tack and rinse the figure under the tap to remove residual flux.
Hope this helps, but if all this sounds a little risky, or is a bigger investment than you want to make, then a good two part epoxy, such as devcon or araldite, will probably give a good enough bond. It will certainly be better than cyanoacrylate, which has no real shear strength in my experience.