breifly mention him in a sentence, like a small preview! have him be mentioned ever so slightly in...maybe the 2nd chapter (depending on how long your chapters are like if the first one is only a page or something do not put him in the first chapter but if its like 20 pages maybe stick him in on the eighteenth page.) however your writing it. btu do it ina descrete way that he isnt given away, make it creative. let the reader be shocked to know that he is the romantic lead! dont describe him in a way that makes him seem desireable, leave it flat and open to opinion. hope this helps.
and introduce whichever character you want to focus more on, first. unless your doing them equally... start with the girl. romance novels are typically geared towards girls and the reader will be pleased to find someone they can relate to in the beginining.