|If like me, you prefer the look of a lapped zipper to a centred one then you might find this tip helpful.
When cutting out your fabric, add a bit extra to the seam allowance on the seam that the zipper is going to be inserted into.
I usually add 0.5 cm making the seam allowance 2cm in total (this would be about 1/8inch or a 3/4inch total seam allowance in imperial).
This gives you a bit of extra fabric to play with and is especially helpful if you have a thick or bulky fabric.
I also apply iron on fusing to the zipper area, usually just a bit wider than the seam allowance and length of zip which stops the fabric distorting.