use liquid flux when tinning wires...then heat post until solder pools up in recess on top...then reheat and hold tinned wire in pool of solder until wire and solder on post melt together...that's not the easiest esc to solder but just practice..liquid flux helps allot when tinning and having a properly tinned wire makes it much easier

make sure you wipe tip with wet shop towel after every time you touch solder to the tip...