It should be wet enough so that it can be easily packed. Test this by taking some snow in hand and making a ball out of it. The ball must stay together and not crumble easily.
Also, one needs to understand that the top and the middle balls of snow need to be lifted up and placed on top of the lower balls. Hence, the size of the snowman should be decided keeping in mind the number of people who are building it.
As you roll the ball, more snow will stick to it. Press this snow firmly onto the ball. Roll the ball in all directions so that snow sticks to all sides and what you get is a good spherical ball that is equally round on all sides. This is the bottom potion of your snowman.
Place this ball in a place where you want the snowman to stand. You definitely don't want to shift the position of your entire snowman after it has been made. Scoop some snow out from the top in the center of this ball so that the next ball can be placed comfortably over this one, which will form the lowest portion of the snowman.
Now, make the middle portion of the snowman. This is as we call the "heart and soul" of the snowman. Start the same way as you did while making the lowest ball. Take some snow in hand and make a ball by it together.
Now, roll the ball over in all direction and press the snow that accumulates around it, but remember that this ball has to be smaller than the lowest one, say about two-third the size of the lower ball. Also, be sure that the snow in this ball is clumped tightly together. You do not want the snowball to crumble when you are placing it over the other ball.
Make a hollow at the top in the center as you had made in the previous ball. Now, gently place this middle ball over the hollowed area on the lowest ball. Put some more snow around the place where the two balls are in contact. Press the snow firmly and clean out the extra to give a clean look to the meeting edges of the two balls.
Place it on the scoop that is made on the top central portion of the middle ball and seal the joining place with some tightly-packed snow and remove the extra amount.
For the face, you can arrange pieces of coal, pebbles, or rocks into a smile. For the nose, the most common option is to use a carrot. Alternatively, one could also use a fir cone, tangerine, or anything else that you wish to choose. Only be careful that while inserting these objects the snow ball does not crumble.
It is better to have the sticks slanting slightly upwards or downwards than sticking right out of the sides horizontally. In case you want your snowman to hold a broomstick, ensure that the end of the stick is buried a few inches below the snow.
This is to ensure that it is not blown away by a strong gust of wind. Also, be careful while inserting the stick into your snowman. Just as with the nose, the snowball may crumble if the sticks are inserted in haste.
Ensure that you tie the muffler into a neat knot so that it stays where it is supposed to. You could also put some leafy branch of a tree as hair. If you are planning to provide your snowman with a hat, consider knit hats, as they are better options than top hats that tend to be blown away by wind if not secured. Scarves are also a good alternative to hats.
This was just one of the ways for those who want to know how to build a snowman. Alternatively, instead of using two balls of snow for the body, one could just make a single mound and place a round ball of snow on top of it for the head.
As far as decorating and giving a real look to your snowman is concerned, the sky is the limit. Enjoy your winters holidays and build your own snowman!