Reducing bulky seam allowances really make a difference to the final look of the garment. It's definitely not worth skipping this stage!
Here's how I like to reduce bulk seams inside my garments.
1. Sew your garment as per the pattern instructions. Below is a neckline sewn with a 1.5cm seam allowance.
I like to start by trimming the seam allowance down by about half. If your seam allowance is smaller then you won't need to trim quite as much.
This basically means trimming just the lining or facing part of the seam allowance down again by around half.
3. Notch or Clip
Notching or clipping the seam allowance means that there won't be any pulling on the outside of the garment and it helps to get necklines and other edges to lay flat.
For an inner curve notch (remove small triangles) and for an outer curve clip (small snips). Make sure you don't go through the stitching.
Flatten the seam with the right side of the fabric facing you. Push the seam allowance towards the facing. Then stitch on the right side of the fabric, on the facing/lining part, just a few mm from the seam line. This will encourage the facing or lining to stay on the wrong side of the garment.
Press the seam carefully, using a pressing cloth if the fabric is delicate or has a tendency to look shiny. A clapper is great for getting a nice crisp edge. Apply heat to the garment and then hold the clapper on the neckline to hold the heat in the garment as long as possible. This creates a permanent crease.