What are some guidelines to creating a summer menu at a restaurant?

I'm a line cook at a restaurant ($16-22 plates) and my exec/mentor is less than forthcoming with all his knowledge about the culinary arts. Our menu is pretty static and he told me he doesn't plan on changing it because he is moving out of the state soon and doesn't care. Well, his job might fall to me and I would like to change things up a bit. Summer is here and I would like to add/replace some items that are more fit to the season. I figure more salads, fruit, maybe a cold soup with less cream sauces and heavy, thick foods. I'm not really looking for specific recipes as such, but more of a guideline on what to include and not to include. Thanks!