It is recommended that you clean dirt off your tools regularly and store them under cover, in a dry place.

Many gardeners will clean them and then run them into a bucket of sand and a bit of oil to recoat them after use.

Pruners and other blades do best with frequent sharpening and a bit of oil on the hinges.

If the tools are severely rusted, it may be unsafe to use them any longer; if they are slightly rusted you might try a bit of steel wool or perhaps a dab of rust remover (check the label directions to see if it is appropriate for the metal in question).

Another option is to brush off the rust as well as you can and then use a rust inhibiting primer and paint according to the label instructions.