2nd...add horizontal pins and secure vertical pins as you go
Allow the pins to hang out the back until you get to each one in turn. The next pins you add will run horizontally, joining the seamlines in front and back together. The pins will run right next to the paper edges or, if you have traced around the pattern first, along the pencil line.
Working from left to right:
(Pin #1) Secure a pin horizontally along the seamline immediately to the right of the beginning pin.
(Pin #2) Secure the beginning pin vertically.
(Pin #3) Secure horizontal pins along the line (as many as needed), each one to the right of its neighbor, until you reach a match point or the end of the seam. I usually pin close enough so they are almost head-to-tail. The longer the seam is, you can often put a little more space between them.
(Pin #4) When you meet a match point, put in the horizontal pin to its right and then secure the match point vertically. If this were a longer seam, continue pins horizontally to the right.
(Pin #5) Secure the last pin horizontally along the seam line. The seam is ready for sewing.
Basically: the first pin and match points are always vertical. All the rest are horizontal.
When you sew the seam, sew slowly from edge to edge immediately next to the paper pattern. Do not pull the pins out early-- as the needle gets to the sharp end of each pin, hold the head of that pin up lightly and the fabric will feed right off the pin as you sew, helping to keep the seam exactly as you have pinned it.
PAPER PIECING FINE POINTS
These are my suggestions for faster, easier, and better paper piecing.
Good pinning ensures accuracy. My pinning method works well for both curved piecing and paper piecing--use it whenever you need to pin along the edges of a pattern when joining sections.
1st...get first pins parallel
Bring together two sections that will be sewn together. Pin through the beginnings and ends of the seamline you will be sewing. Also add any pins that join match points (the facing arrowheads on Paper Panache patterns, or the hatch marks in machine curved piecing). (See Pinning Matchpoints below.)
The drawings above left look down between the two pieces of fabric from above. Slide the fabric around minutely until pins line up parallel to each other (see second drawing). Push pins in most of the way and leave them hanging, pressing the pieces together with your fingers. Turn the seamline back to face you.
Pinning at the points
When pinning sections together that begin or end with the point of a triangle, place the pin immediately ALONGSIDE the point (vertical arrow), and not at the very tip of the point (horizontal arrow). The difference is tiny, but pinning the rest of the seam should be easier and sections line up better.
Pin with multiple seams UP
When pinning two sections together, you have a choice to pin from either side. Sewing is usually a lot smoother if you place the section with the most seams "on top" and pin from that side. The side with the fewest seams would be the side that travels over the feed dogs.
Pinning match points (matching arrowheads)
The arrowheads in the pattern show where two seams (or a seam and a designated spot on another section) should line up when pinning. If the arrowhead is on a seamline, put your pin through the side of the seam with one layer of fabric and not through the side with the seam allowance, right at the point of the arrowhead. Match the arrowhead to its partner by pinning through the single layer of fabric on the other side, making the arrowheads meet. Occasionally seam allowances will make matching through one layer difficult or impossible; just do the best you can.
If it appears you have "lost" or "can't find" a matching arrowhead, first check your piecing order and make sure you're joining the correct sections together. If so, you'll probably find the "missing" arrowhead hiding under a seam allowance.