You probably shouldn't wear sunglasses if you want a good tan because it makes you less tan. Your pituitary gland that release the melanin hormone is connected to optic nerve in the eye and is activated less when you wear sunglasses. What I do is wear my shades for like 8 minutes and than take them off so that my eyes can get adjusted to the sun better.
There are some hidden secrets you guys should know about sunscreen as well. This article does it great job exampling this: