In the dressmaking process, it is crucial that all sewing patterns are cut perfectly on grain. Ensuring that all pieces are cut on grain will not only result in a high quality garment, it will also provide the necessary comfort and fit designated for it the garment's design.
Luckily, aligning sewing patterns on grain is fairly easy to do with the help of a double-pointed arrow called grainline. Every paper pattern should feature a grainline which is the very first element aligned and pinned in the fabric cutting process. Once the grainline is properly aligned and pinned, the rest of the pattern edges can be easily secured with pins knowing the pattern won't shift off grain in the process.
Strat the pattern pinning process by inserting a couple pins along the grainline catching the fabric layer(s) underneath. Be mindful of your fabric- if you are working with highly sensitive fabrics that can be easily damaged by pin pricks, use fabric weights instead.
The ensure the pattern is aligned on grain, use a ruler to position it perfectly parallel to the fabric selvage edge. The easiest way to do this by first, inserting a pin on one end of the grainline and measuring from this point to the selvage edge. Next, shift the unpinned end of the pattern such that the grainline at this end is now at exactly the same distance from selvage edge. Insert a second pin to secure the pattern perfectly on grain.
Using this technique as a preliminary step in the pattern alignment and pinning process will ensure that your patterns remain accurately on grain through the remainder of the pinning and cutting process.