Here I've selected a 22x30" sheet of Arches Cold Press #140 paper and am wetting it liberally on BOTH sides with clear water which helps to keep the paper flat while you're working, and wet enough so that the paint will move on the paper. While it's wet, if it creates ripples, simply lift one edge and pull slightly to smooth out again.  Don't touch the top of the bubble as you will leave fingerprints which will show up later.

While the paper is drying to a light sheen, I select the tubes of watercolor paint I wish to use.  Generally using two or three colors is enough, especially for beginners. Choose colors you LOVE, keeping in mind what they do when they mix together. (i.e., mixing complementary colors usually creates mud)   I use Daniel Smith or Windsor Newton paints almost exclusively, however beginners can use a student grade paint like Grumbacher Academy or Cotman

In a small cup I mix about a 1/4 to 1/2 inch squirt of paint directly from the tube (about the size of your pinkie finger from tip to first knuckle).  If you're using a 1/2 sheet of paper, use the smaller amount.  Then add about 1T of water.  I squirt it in with a spray bottle, a little at a time.  You want the paint to be fluid, but not watery...like milk or cream.

I mix all of the paint cups before pouring.  So, if the paper has become a bit dry (lost it's sheen), I may mist it lightly with my fine mister bottle, then begin the pouring process.
As you begin the pour, you must be thinking about design principles.  Often the cruciform is the best pattern.  Some people pour with a subject in mind, I choose to think DESIGN. As you can see, if you pour directly down, you get a round shape...if you move your hand while pouring, you can get the paint to move out into a line and fill the page more easily.
I usually use all the paint from each cup.  I choose the darkest color first, adding the lighter ones on top.  Doesn't always work that way, depending on the pigment.  You have to experiment.

As I add the next colors, I am following the first pattern laid down by the first color. Overlapping some, but mostly keeping them close to one another

Same thing for the 3rd color.  Since my choice for the 3rd color in this case is Naples Yellow, which is slightly opaque, it will sit on top of the French Ultramarine Blue and Quinacridone Burnt Orange, and actually push those 1st two around