Turn on your soldering iron. If your soldering iron has temperature control:

Set it to 350 °C (~650 °F) if you're using leaded solder

Set it to 400 °C (~750 °F) if you're using lead-free solder

Clean the tip of your soldering iron. If you're using a sponge, wet the sponge and quickly wipe the tip across it. If you're using brass wire, stab the tip into the wire a few times.

If you're not using solder paste, melt a small amount of solder onto the tip. You'll transfer this solder onto the joint.