Are you talking about the fabric raveling? Or about the thread tails from where you start and stop sewing? If the later, do you use a starter/ender tab? I find using one reduces the tread trimming dramatically.
A starter tab is a small scrap of fabric that you start sewing on and then you add your fabric, as in the first piece of a chain stitch. When you trim off the starter tab, your string problem is gone. Then, add another scrap at the end for an ender tab...which now becomes a starter tab for your next seam.
When using the starter/ender tabs, as in chain stitching, leave at least 4 stitches between your patches. This will give you a space to cut and also give a stitch or two to give a lock stitch to help the seam from separating.
I hope this is clear. It's easier to show than to explain.