Wear clothing which feels comfortable & warm enough for the conditions. Shorts and a t-shirt will suffice in warmer weather conditions. When it gets colder think about layering - perhaps a long sleeved t-shirt and a wind- or rain-proof jacket. Full length running tights are also an option. Sports manufacturers have developed specialist fabrics that provide "moisture management" - drawing moisture (sweat) away from the skin - to keep you relatively dry during your runs. Your local specialist running retailer will have a range of products and will be able to offer advice and answers to any questions you may have.