Just as hygiene is imporant for humans in order to prevent the spread of diseases, so too is hygiene important for your garden. I'm not talking about washing your hands, although you should do that for your own health, I'm talking about special things you can do when gardening to help keep your garden healthy
To prevent tools from rusting, rub them with a bit of vegetable oil. This is especially important if you've been pruning something with a high sap content as sap is very corrosive.
If you use any tools in your garden other than your hands, it can be a good idea to wash them well after each use and when you're using them in different areas of the garden. The reason for this is that if the soil in one area of your garden becomes infected with a fungus, bacteria or a virus, soil from your trowel for example, can carry the disease to other areas of your garden. If you remove the soil from your trowel before moving to a new area of the garden, you greatly reduce the risk of this kind of disease transmission. Tools can also spread weeds if not cleaned in between uses. For digging tools, washing with water, or maybe water and detergent, is fine.
Of greater importance, is the proper care of cutting tools such as secateurs. If you prune a diseased plant and then prune a healthy plant with the same secateurs, without cleaning them in between, the disease will very easily spread to the healthy plant because it can be transmitted directly into the plants vascular system. It just like when you have a cut. If you touch the cut with something dirty, pathogens can enter your bloodstream directly.
If you've been pruning a plant with a high sap content, methylated spirits, turpentine or eucalyptus oil can be used to help remove the sap residues.
To clean your cutting tools, as a minimum, you should wash them thoroughly with soapy water. A safer bet, is to wash them with either bleach, alcohol or tea tree oil (or another natural disinfectant) to ensure you kill any pathogens. You should definitely do this if you have been pruning a plant that you know is diseased.
If you use your lawnmower to cut multiple lawns (perhaps you have a lawnmowing business, your child mows lawns for pocket money or you have an allotment or community garden plot as well as a home garden) make sure you remove all the left over grass otherwise you may spread weed seeds.