First off, if you're not in the habit of cleaning your pruning shears, you may be asking why this is necessary. Diseases can spread from plant to plant easily through your shears. As well, clean shears will work better, and more efficiently by keeping them sharp and cutting the plants clean without crushing the stem. Washing your shears in a diluted bleach and water solution will help to disinfect, and a scouring pad or steel wool will help with the hard to remove grime. Contrary to a lot of misconceptions, bleach is not harmful to your plants in a diluted solution, and in fact it helps to prevent bacterias. Happy pruning!