I usually do In The Pot (ITP)Swirling. You take out portions of your soap that you colored, and then after you mix the color, you pour it into the POT going around and then you pour into the mold. I save a little color and then swirl on the top too. Here are some of my ITP swirls.
It is best to mix colors at a VERY VERY light trace. That gives you time to swirl before it thickens up. This soap was an ITP Swirl, but the white base (which was scented with a fo that can accelerate) thickened up before the colored soap that was not scented and it gave this marbled look.
This soap I kinda did layered swirls. What that means is I poured some green color on the bottom of the mold then white then green again and alternated. This was at a very thin trace and I kinda just took my butter knife and ran it up and down to drag the colors.
Other tips for swirling besides mixing a thin trace
If using powdered colorants, mix with a tiny bit of oil or water before adding your raw soap.
Don't over mix the colored portions so that it gets thicks, then you get globs.
I take out 2 cups of raw soap to color for my 15lb batch. Half is way too much.
Unless you have globs, don't over stir the swirls because then you loose that defined look.
That's all I can think of for now. There are a lot of you tube video's on soap swirling.