A couple of things about soldering:
1.) Try to utilize the "2 Second" rule, meaning, you should never apply the iron for longer than about 2 seconds.
2.) If you properly 'tin' the points where contact will be made, apply a small bit of solder directly to the iron, join the pieces to be connected, and apply the iron. The solder on the iron will react quickly to the solder on the joining pieces, it will melt quickly and you remove the iron.
3.) The fumes from soldering are toxic, therefore do this in a well-ventilated area.
4.) Check appearance of the solder joint. If it is dull and gray looking, you have what's called a "cold solder joint", and is likely to either fail eventually, or not provide good continuity. Redo. You're looking for a smooth, shiny, silver appearance.
5.) Don't fall into the notion of "The bigger the blob, the better the job". This is not only wasteful, but is contradictory to good soldering practices, and could lead to short circuits (especially in those tiny 3.5mm connectors).
6.) Practice, practice, practice...
Hope this helps.