The three most important characters in a romantic suspense are the heroine, hero and villain. You need each one to have a romantic suspense.
Let’s start with the heroine. With each character you should develop their background. From that background you will come up with their present goals and motivations. Then you throw in a conflict or two to get in the way of the heroine obtaining her goals. It is paramount that you throw roadblocks up for the heroine. That is what drives your plot both internally and externally.
So what kind of heroine should you have? In today’s market most heroine’s are strong and can deal with a lot of difficult situations. Gone is the heroine who needs to be saved every time you turn around. I often write one who will do the saving as well as be saved. In Heart of the Amazon Kate saved Slader a couple of times even though the jungle was his domain. When they slid down a side of a mountain in the rain, it was Kate who kept Slader up all night because he had hit his head. She didn’t want him to fall asleep because of the threat from a concussion.
I have so much fun writing my heroes. Personally I read a book and focus on the hero. The heroine has to be acceptable, but the hero is what makes or breaks a romance for me. Like all characters you do not want one who has no flaws. Both the hero and heroine should have flaws. They should grow through the book and learn and change. What they experienced through the story makes them a different person.
Almost as important as the hero and heroine is the villain. Above all, try to make your villain as three dimensional as possible. Give your villain some good qualities as well as bad ones. People aren’t all good and they aren’t all bad. So remember that when you are developing your villain. Give him a family he loves or an animal he takes care of. Think of Darth Vadar in the first Star Wars and the one in the last one. As we got to know him and got glimpses into his background and what made him tick, we saw a more three dimensional character. In the first movie he was all bad, intimidating. I suggest you do a goal, motivation and conflict chart for your villain, too.