Lavender is a desert plant, basically, so just do not leave it in a low-lying area where the roots will be in muck and do not place it in an area with poor air circulation if the air is humid - place it in a higher and more open area and be sure it gets plenty of sun and wind to make it happiest. Also you should cut it back after it flowers - there will be a dead-area on each stem and more fresh growth below that, so by cutting the stem at the dead-area and just above the new sprouts, it makes the plant look better and stay more vigorous (plus then you have the cuttings and flowers to scent something.)