I'm a lazy old coot. I've patched hundreds of tubes, from 16" bikes to heavy trucks and farm tractors, and I haven't sanded a tube in the last forty years. Most auto part stores sell a product used to prep tubes. Magic Buff is one, NAPA calls theirs Liquid Buffer. I buy a pint every ten years or so, put an ounce or so in a small plastic bottle, and carry it on the bike. To patch a tube, clean the area around the hole with the liquid on a paper towel, smear on a thin coat of cement, let it dry a couple of minutes, apply the patch and press it down. The only failure I can remember was when I missed the hole with the patch.