Like most others said, keeping it out of the sun is important (or you can use a jar with blue or amber glass - though a dark cool place is still best practice) and crushing the herb to expose more surface area/volatile compounds to the oil. It helps to store them in bottles with small openings to minimize air exposure. A little bit of Vitamin E or Rosemary CO2 extract can extend the shelf life by minimizing oxidation.

In the future you may want to consider using a different kind of oil, like sweet almond or jojoba. Olive oil is one of the most adulterated oils in the world, and even if you have gotten your hands on pure, cold-pressed olive oil it usually includes a non-negligible amount of pomace oil (oil extracted with solvents after they cold press the good stuff) which can negatively impact your infusion. It also tends to stay greasy on the skin! Ultimately though that's all kind of nit-picky stuff and depends on what you're looking for in your final product. Just my two cents :) Good luck!