It is always a rule in fashion that one should consider her or his own personal style in following the trend. But more be specific I can give some fashion no-nos just for example you have in this picture.
A sandal should not wear with white sacks or sacks that is a big no-nos. Never wear sandals as well with trousers. Sandals are more flattering when wear with shorts short for women or jeans skirt and for men walking shorts but please no white sacks or other colored sacks..
Second no-nos example: Do not overwhelm your self with too much color and accessories. Golden rule in fashion is that Less is best fashion statement. when I say Less meaning to say that tone it down,by balancing the color with the right pair of shoes or bag and accessories. For example you are wearing floral print dress tone it down by wearing solid color shoes or bag/clutch bag. and if your wearing necklace don't wear watch or bracelet anymore, just necklace. If your wearing silver never mix it with gold accessories.