Use a stiff-bristled brush or pressure washer to remove algae from paths. A proprietary algae killer may help.
Remove dirt and algae from walls, paving and patios. Pressure washers can be rented if necessary.
Check and repair pergolas, arbours and arches if needed.
In dry spells, you can treat timber structures with wood preservative and stain. Only do this in a well-ventilated space, to reduce the risks to your lungs and eyes. Make sure you use appropriate products. Creosote, for example, is no longer legal (link to page on products taken off the market).
Go through your shed and remove any old, out-of-date garden chemicals. If in doubt of how to dispose of them, your local authority tip should be able to help.