Using an Invisible Zip Foot makes this so much easier. There are two types available:
1. A branded make for your machine.
2. A universal one that will also make sewing normal zips much easier than using the ones that are often supplied with your machine. It allows you to stitch past the zip pull. This can also be used for making piping.
1. Neaten the edges of the fabric, but do not stitch the seam.
2. Tack the seam on the stitching line, carefully matching the fabrics design and any seams that cross in the zip area. The photo shows the needle being used to match the pattern exactly. Press open the seam lightly with your fingers
3. With the fabric RS together open out one seam allowance. Place the zip with WS on the top, the teeth exactly on the tacked seam and the slider 2mm below the seam line. Pin the zip tape to the seam allowance.
4. Draw a line on the WS of the zip tape 2.5cm above the end stop. Use chalk or fabric marker that will not bleed when washed.
5. Stitch the zip tape to the seam allowance. I have used a zig zag stitch, but a straight stitch or very small tacking can also be used. STOP at the line you drew on the zip.
6. Repeat stage 5 on the other side of the zip, stitching the tape to the seam allowance.
7. Using small stitches tack close to the zip teeth through the tape and seam allowance on both sides of the zip.
8. Remove the first line of tacking that held the seam together. Fully open the zip.
9. Attach the zipper foot to the machine. Select straight stitch. It is important to stitch as close to the teeth as possible.
10.  Look carefully at the photo to see how the zip is placed under the zip foot. When stitching to the right of the teeth the zips coils are under the left groove.
11.  The ‘toe’ on the front of the foot helps to open the zip teeth. I find its best to put a finger on the teeth to hold them open. Stitch slowly, stopping exactly at the line you marked earlier.
12.  Stitch the other side of the zip, repeating stages 10 & 11, using the other groove in the zip foot.
13.  Close the zip to check you have stitched close enough to the teeth and any patterns and seams still match.
14.  Fully open the zip.
 Stitching the seam.
15.  Where you finished stitching the zip, stab a pin through the fabric to match with the end of the stitching on the other side of the zip. Keep the end of the zip tape out of the way. Pin the seam.
16.  Use a standard zip foot to stitch the seam near the zip.  The zip is still open, keep the bottom of the tape right out of the way. Start about 3cm below the zip and stitch up to the pin you stabbed into the fabric. The threads need fastening very securely.
If this proves too tricky use a very small hand stitch for this part of the seam. (about 3cm). Back stitch is best.
17.  Use the standard machine foot to finish stitching the rest of the seam.
18.  To fasten the zip, push the zip pull through the space at the bottom of the zip. Hold the pull in one hand and the bottom of the zip tape in the other. Pull firmly, but carefully, to close the zip. Take time to make sure the fabric doesn’t roll into the zip teeth.
19. Press on the RS.
On the inside the bottom of the zip should move freely. 
You can cover the end of the zip. If your fabric is bulky use a strip of lining fabric approx. 4 x 8 cm.
20.  Press 5mm to the wrong side on each edge.  Stitch one short edge to the zip.
21.  Fold the strip of fabric over the end of the zip and stitch round the edge.
On the right side you should have what looks like a seam in your fabric, with only the zip pull showing.