The single most important thing to look after your umbrella and prolong its life is to invest in a good quality protective cover. An umbrella spends most of its life folded up not being used. If it is enclosed in a cover it will remain clean and looking like new for many years.
Bird droppings and environmental grime can be removed by hosing and scrubbing with a soft brush. Never put the cover back on if the umbrella fabric is damp or wet.