If your goal is to maximize your Open Rate the best thing to do is to work on a subject that the user can find interesting so that the subscriber is more likely to open your campaign. Avoid repetition, symbols, with reply at the beginning of the subject (“Re” or “Fw”), writing in Caps Lock and spam words.
Other thing is to insert the city’s location where you’re directing your campaign (for example: Offer just for Residents in Paris!) – t
Take a look at Writting Killer Subjects to know more techniques to write a good subject!
But if you want to maximize your Click Rate, place a Call-to-Action in a visible part of your campaign and above the fold, with a distinguishable color, so that the subscriber can see it right after he opens the email and that he doesn’t need to scroll to see it.
Another option to maximize your click rate is to keep it simple, by building an email kit that is attractive and simple enough, without too many distractions.