Most pet owners do not want the length of a show dog (which is scissored rather long) so I use a 1 or 1 1/2 snap on over the body, starting about two inches behind the occiput. Leave the entire head full from a line at the back of the jaw and meeting your neck line at the back. The body is then scissored over. Porties technically come in two coats, the wavy and the curly, but you also find some described as "loose curly" which fall somewhere in between. Keep in mind the curlier the coat the shorter the snap on will cut. When in doubt start with the #1. The legs are scissored fuller, much like you would do a poodle, but with full feet. Front legs should be straight columns, rear very tight at the anal area and down the back of the leg to about 2" above the hock, then longer from the hock down to build some angulation. The front and sides of the leg are longer, blended smoothly all around. Also clip the top 2/3 of the tail with the same snap on, leaving the end untouched in a "flag". This is then scissored in so it is slightly wider at the base than at the start of the flag.
The topline is supposed to be level, so in scissoring over your snap on work make any adjustments needed such as correcting a steep croup or roached back. (Both are a fairly common faults that can be scissored out) Many Porties are also very close behind and need to have the iside of the hock scissored shorter than the outside to give some space between the legs. (Both of these comments are more for show dogs, but I "fix" the pets, too.)
The head is the most unique and difficult part of the breed. Be careful on wavy coats as they tend to cowlick and too big a snip at one time can send the hair the wrong direction. The topknot is shorter that a poodle, fuller in front for a slight recess to the eyes, but many pet owners want to see more eye. Bichon like, the top is blended into the ear coat, there is no break. The ears themselves are scissored rather round, very close to the leather at the tip and 1- 1 1/2 inches at the sides. Once the outline is set, the inside of the ear is scissored to blend smoothly and the out side is scissored to blend with the sides and into the topknot. No more than 1 inch of coat is left on the outsides of the ear. The back of the topknot is blended smoothly into the neck (no break) using that two inches you left in your patterning. The breed is supposed to be short necked, the extra thickness on the back of the neck helps give that impression.
The muzzle is scissored differently depending on the type of coat. The wavies need more length than the curlies. Start with the lower jaw and scissor a straight line which starts about 3/4 of an inch below the front of the lower lip and continues to the back of the mouth ending about 1/4 inch below the jaw. (In other words, there is more hair at the front of the lower jaw than at the back, but the line is straight, not curved.) Once the lower lip line in in, scissor the bottom edge of the muzzle hair to match. Don't curve from the front of the lips, just scissor a straight line back. On a wavy, looking at the muzzle from the side, comb the front of the muzzle hair forward and remove any coat which extends beyond a straight line from the tip of the nose square with the bottom of the muzzle you just trimmed. The muzzle is mostly done except that on some dogs you may want to thin out a bit under the eyes so that when viewed from above the muzzle is square, not wedge shaped. On a curly, use the comb to pick up the hair all around the muzzle and scissor around the top and sides of the muzzle to create a cylinder. Scissor the hair out from the bridge of the nose. Pull the hair at the front of the muzzle forward and scissor straight to form the bottom of the cylinder.
Next scissor out the neck where it meets the jaw. You can use a 4 blade to get the length here, about a two inch triangle at the top of the neck at the jaw blended into the rest of the neck hair. The sides of the face are next. Pull back one ear and look at the dog head on and scissor the cheeks so that they blend in with the topknot creating a large round head. Think of it as a bowling ball, and the bottom of the ball is at the jawline, you'll have the correct set on of the head. Watch out on wavy coats that you don't get too short here, it will flatten, and you want round. Pull the ear forward toward the muzzle and scissor the hair behind the ear to continue your "ball" into the back of the topknot you've already blended into the neck. Repeat with the other side. The overall finished effect is that of the bowling ball having a tin can attached to it at the bottom: Side view: Front view: _--_ _ ---- _ / \ / \ / /--- / . . \ / /---- \ /--\ / | \ _\__/_ / | | Hope this helps and excuse my poor "drawings" Would send pics if I knew how! This is a tough one to describe!