63/37 is considered perfect. And its readily available. You really shouldn't use the solder with silver content. It has no electrical benefit. Its there only to raise the melting point. Good for circuit boards that lay next to jet engines - bad for newbie guitar soldering.
Add enough solder to form fillets (rounded curves) between components. You should be able to barely distinguish separate wire strands (with solder filling in and rounding out the gaps between the strands).
If the wire and connector are hidden under a blob, you’ve used too much solder.