The leaders - sew one pair of scraps together, chain-piece the fabrics you're working on, and at the end of the pieces you're putting together, use another pair of scraps chain-pieced to finish up.
I leave the 'ender' in my sewing machine - becomes my 'leader' for the next seam/chain.
I find this stops the beginning seam getting eaten by the feed dogs, stops the 'birds-nest' effect when threads wander and get caught up. It also stops me from wandering at the beginning or ending of my seams (I used to have terrible seams as I was getting to the end - veering off into a narrow seam). And the thread trimming is almost non-existent!
So, here's what I'm doing ...
- have a little container of scraps handy - 2" squares? strings or strips
- pick a light and dark, start a chain and piece these scraps
- the next pieces in the chain-piecing are the current project you're working on
- finish up with another pair of scraps - the ender- leave these ones under your machine foot (I leave it down, but the needle up). This one becomes my 'leader' for the next pieces I'm sewing.