When I was young, I would say that simply waking up in the morning made me motivated the rest of the day.
Perhaps you are asking a different question, "what can I do to make sure that my marriage is a success, sexually?" If I could give advise along these lines it would be, be selfish.
This does not mean that you should not be loving, or cater to his desires, but that you should try to find things that you enjoy. For example, generally speaking, women take longer to be fulfilled than men do, so I suggest you experiment with delay tactics that keep your partner interested, and get you going.
This involves roll playing. Very few people want, wham bam, thank you mam. Most people I know want to be portrayed in someway in order for them to enjoy some fantasy. Generally speaking but not always, women want to be wooed, courted, praised, pursued, or fondled. With men, some men like submission, boldness, a challenge, flirting, titillation, (this is a long list). Something should be said about fetishes, it is likely that your husband will have one. [Examples of fetishes are feet, latex, domination, school girl or child fantasies, homosexuality (in bi or heterosexuals), pain, animals] I would strongly suggest you be sensitive to his fantasies as you have no way to gauge how important they are to him, I doubt he will tell you right out about it, find a way to compromise so that he gets what he needs so you can get what you need.
In my experience many women try hard to please their husbands, at their own expense. Guys love being catered to. But guys want a whole lot more to be good lovers to their wives. Try to guide him in what makes you satisfied, more than trying to be "like they are in porno films", because if you are not happy and your guy does not know why, nothing else is going to work well in your relationship.
Do not worry about how your body looks. Because first, you can't change it, and second, your guy already knows what it looks like, and third, it will distract you from the task at hand. Yes, guys walking down the street measure women on a sexual appeal scale, but it is simply foolishness, it means NOTHING. Sex is at least 75% mental, and if the mental part works then the body part for sure will. Don't worry if you are a little over weight, pregnant, sagging parts, uncombed hair, no makeup, or dark skin, your lover is not thinking about that.
Sex is about him selecting you and vice verse for intimacy. It is about sharing love through giving pleasure. It is about bonding. Sex is often called making love, because, if you are honest during and after having sex, love follows and builds.