The reason that sexual attraction is easy at the beginning is because it's new. As time goes on though, the newness wears off so I think that's the place to start.

1. Make it new again. Set up a role-playing date where you both take on different personalities. You can be an entirely different person and you can both meet over coffee and talk though your new personas in a role-playing manner. Rediscover each other!
2. Change it up. Hook up with each other in different places. The bedroom at 9:15 PM on Tuesday gets old so how about 11 AM on the washing machine? Or in the car while driving to Sunday dinner?
3. Go shopping at an adult store. Adults need toys too!
4. Send dirty messages. Sexting your partner while they're at work can add a shock to your day and get you both going for later.

So there's plenty of ways, but I think it takes active participation, not just waiting for the attraction to come back. Go get it!