You failed to mention if you wanted to spice double braid or twisted strand rope, but both “how to”s were given in the thread.
When splicing twisted strand rope (docklines), role the splice between the palms of your hands while pressing hard. This little trick will tighten the splice as you are doing it. I generally roll the splice about every 1/3 of the splice length. When completed roll the splice on the deck using you’re a flat sole shoe.