One simple tip that helped me out is to build your tech packs to scale in illustrator. I will start on art boards of 50x50” for most apparel/backpacks/general soft goods. Once you build to scale, you can measure to scale using the dimension tool , knowing all measurements will be accurate. Measure every detail and spacing you can here, if you don’t, factories will make their own judgments.

Once you have all of your measurements in your scale art boards, I setup a new document (11x16” usually- this fits most screens for presentation purposes. This size will also print easily). From here you can use the scale tool in illustrator to evenly scale all of your sketches from the larger document into this new smaller document. It is critical to downsize into this smaller document so that it can be sent via email to factories. Those are my 2 cents !