The biggest mistake I see people make with soldering irons is thinking they can "creep up" on it.
This can be especially bad with low watt irons on heavy terminals. There are some tricks to get around this though.
First, it is essential that the tip is properly prepared and tinned. If the tip is not properly tinned, you can not transfer the heat to the part and it will require too much contact time. There are plenty of good videos on this subject, they all pretty much have the same theme, add solder and scrub it in with a brush or brass wool until it is evenly coated.
Soldering also requires really good contact with the part, so do not be afraid to use some real pressure and twisting/scrapping motion to get the tip in good contact with the part.
Start by tinning the wire, get a good even coat, try not get too blobby. Next apply the tip to the terminal, dab the solder around where the tip meets the terminal until it starts to flow and get a thin coat. Now touch the iron to a wet sponge, this will cool the tip and force the iron to run at full heat, apply the wire to the terminal and put the iron against the wire until the solder starts to melt, and then drag the iron around until it contacts the terminal and melts the solder there. Remove the iron and do not let the wire shift even in the slightest until it changes color.
I have a nice Hako iron, and I run it about 450C when I do this work. This is way higher than typical soldering temps, but it lets me get in and out very quickly. Being quick is the key, so either run at very high temp, or use a high watt iron.
For audio stuff, I use Cardas silver solder. If you see it cheap on Amazon or Ebay, is almost certainly counterfeit.